chapter 2 differentiation · chapter 2 differentiation section 2.1 the derivative and the tangent...
TRANSCRIPT
© 2018 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.
C H A P T E R 2 Differentiation
Section 2.1 The Derivative and the Tangent Line Problem ................................. 114
Section 2.2 Basic Differentiation Rules and Rates of Change ............................. 129
Section 2.3 Product and Quotient Rules and Higher-Order Derivatives ............. 142
Section 2.4 The Chain Rule ................................................................................... 157
Section 2.5 Implicit Differentiation ....................................................................... 171
Section 2.6 Related Rates ...................................................................................... 185
Review Exercises ........................................................................................................ 196
Problem Solving ......................................................................................................... 204
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114 © 2018 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.
C H A P T E R 2 Differentiation
Section 2.1 The Derivative and the Tangent Line Problem
1. The problem of finding the tangent line at a point P is essentially finding the slope of the tangent line at point P. To do so for a function f, if f is defined on an open interval containing c, and if the limit
( ) ( )
0 0lim lim
Δ → Δ →
+ Δ −Δ = =Δ Δx x
f c x f cym
x x
exists, then the line passing through the point ( )( ), P c f c
with slope m is the tangent line to the graph of f at the point P.
2. Some alternative notations for ( )f x′ are
( ), , ,dy d
y f xdx dx
′ and [ ].xD y
3. The limit used to define the slope of a tangent line is also used to define differentiation. The key is to rewrite the difference quotient so that Δx does not occur as a factor of the denominator.
4. If a function f is differentiable at a point ,x c= then fis continuous at .x c= The converse is not true. That is, a function could be continuous at a point, but not differentiable there. For example, the function y x= is
continuous at 0,x = but is not differentiable there.
5. At ( )1 1, , slope 0.=x y
At ( )2 252
, , slope .x y =
6. At ( )1 123
, , slope .=x y
At ( )2 225
, , slope .x y = −
7. (a)–(c)
(d) ( ) ( )( ) ( )
( )
( )
4 11 1
4 13
1 231 1 2
1
f fy x f
x
x
x
−= − +
−
= − +
= − += +
8. (a) ( ) ( )
( ) ( )
4 1 5 21
4 1 3
4 3 5 4.750.25
4 3 1
f f
f f
− −= =−− −≈ =−
So, ( ) ( ) ( ) ( )4 1 4 3
.4 1 4 3
f f f f− −>
− −
(b) The slope of the tangent line at ( )1, 2 equals ( )1 .f ′
This slope is steeper than the slope of the line
through ( )1, 2 and ( )4, 5 . So, ( ) ( ) ( )4 1
1 .4 1
f ff
−′<
−
9. ( ) 3 5f x x= − is a line. Slope 5= −
10. ( ) 32
1g x x= + is a line. 32
Slope =
11. ( ) ( ) ( )
( ) ( )
( ) ( )
( )
( )
0
2 2
0
2
0
2
0
0
2 2Slope at 2, 5 lim
2 2 3 2 2 3lim
2 4 4 3 5lim
8 2lim
lim 8 2 8
x
x
x
x
x
f x f
x
x
x
x x
x
x x
x
x
Δ →
Δ →
Δ →
Δ →
Δ →
+ Δ −=
Δ
+ Δ − − − =Δ
+ Δ + Δ − − =Δ
Δ + Δ=
Δ
= + Δ =
12. ( ) ( ) ( )
( )
( ) ( )
( ) ( )
0
2
0
2
0
2
0
0
3 3Slope at 3, 4 lim
5 3 ( 4)lim
5 9 6 4lim
6lim
lim ( 6 ) 6
x
x
x
x
x
f x f
x
x
x
x x
x
x x
xx
Δ →
Δ →
Δ →
Δ →
Δ →
+ Δ −− =
Δ
− + Δ − −=
Δ
− − Δ − Δ +=
Δ
− Δ − Δ=
Δ= − − Δ = −
13. ( ) ( ) ( )
( ) ( )
( )
0
2
0
0
0 0Slope at 0, 0 lim
3 0lim
lim 3 3
t
t
t
f t f
t
t t
t
t
Δ →
Δ →
Δ →
+ Δ −=
Δ
Δ − Δ −=
Δ= − Δ =
6
5
4
3
2
654321
1
y
x
f (4) − f (1) = 3
4 − 1 = 3
(4, 5)
(1, 2)
f (4) = 5
f (1) = 2
f (4) − f (1)4 − 1
y = (x − 1) + f (1) = x + 1
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Section 2.1 The Derivative and the Tangent Line Problem 115
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14. ( ) ( ) ( )
( )
( ) ( )
0
2
0
2
0
2
0
0
1 1Slope at 1, 5 lim
1 4(1 ) 5lim
1 2 4 4( ) 5lim
6( ) ( )lim
lim (6 ) 6
t
t
t
t
t
h t h
t
t t
t
t t t
t
t t
tt
Δ →
Δ →
Δ →
Δ →
Δ →
+ Δ −=
Δ
+ Δ + + Δ −=
Δ
+ Δ + Δ + + Δ −=
ΔΔ + Δ=
Δ= + Δ =
15. ( )
( ) ( ) ( )0
0
0
7
lim
7 7lim
lim 0 0
x
x
x
f x
f x x f xf x
x
x
Δ →
Δ →
Δ →
=
+ Δ −′ =
Δ−=
Δ= =
16. ( )
( ) ( ) ( )
( )0
0
0
3
lim
3 3lim
0lim 0
x
x
x
g x
g x x g xg x
x
x
x
Δ →
Δ →
Δ →
= −
+ Δ −′ =
Δ− − −
=Δ
= =Δ
17. ( )
( ) ( ) ( )
( ) ( )
( )
0
0
0
0
0
5
lim
5 5lim
5 5 5lim
5lim
lim 5 5
x
x
x
x
x
f x x
f x x f xf x
xx x x
xx x x
xx
x
Δ →
Δ →
Δ →
Δ →
Δ →
= −
+ Δ −′ =
Δ− + Δ − −
=Δ
− − Δ +=Δ
− Δ=Δ
= − = −
18.
( )
( ) ( ) ( )
( ) ( )
( )
0
0
0
0
0
7 3
lim
7 3 7 3lim
7 7 3 7 3lim
7lim
lim 7 7
x
x
x
x
x
f x x
f x x f xf x
xx x x
xx x x
xx
x
Δ →
Δ →
Δ →
Δ →
Δ →
= −
+ Δ −′ =
Δ+ Δ − − −
=Δ
+ Δ − − +=Δ
Δ=
Δ= =
19. ( )
( ) ( ) ( )
( )
0
0
0
0
23
3
lim
2 23 3
3 3lim
2 2 23 3
3 3 3lim
223lim3
s
s
s
s
h s s
h s s h sh s
s
s s s
s
s s s
s
s
s
Δ →
Δ →
Δ →
Δ →
= +
+ Δ −′ =
Δ + + Δ − + =
Δ
+ + Δ − −=
Δ
Δ= =
Δ
20. ( )
( ) ( ) ( )
( )
( )
0
0
0
0
0
25
3
lim
2 25 5
3 3lim
2 2 25 5
3 3 3lim
2
3lim
2 2lim
3 3
x
x
x
x
x
f x x
f x x f xf x
x
x x x
x
x x x
x
x
x
Δ →
Δ →
Δ →
Δ →
Δ →
= −
+ Δ −′ =
Δ − + Δ − − =
Δ
− − Δ − +=
Δ
− Δ=
Δ = − = −
21. ( )
( ) ( ) ( )
( ) ( ) ( )
( ) ( )
( ) ( )
( )
2
0
2 2
0
22 2
0
2
0
0
3
lim
3 3lim
2 3 3lim
2lim
lim 2 1 2 1
Δ →
Δ →
Δ →
Δ →
Δ →
= + −
+ Δ −′ =
Δ+ Δ + + Δ − − + −
=Δ
+ Δ + Δ + + Δ − − − +=
ΔΔ + Δ + Δ
=Δ
= + Δ + = +
x
x
x
x
x
f x x x
f x x f xf x
x
x x x x x x
x
x x x x x x x x
x
x x x x
xx x x
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116 Chapter 2 Differentiation
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22. ( )
( ) ( ) ( )
( ) ( )
( ) ( )
( ) ( )
( )
2
0
2 2
0
22 2
0
2
0
0
5
lim
5 5lim
2 5 5lim
2lim
lim 2 2
x
x
x
x
x
f x x
f x x f xf x
x
x x x
x
x x x x x
x
x x x
xx x x
Δ →
Δ →
Δ →
Δ →
Δ →
= −
+ Δ −′ =
Δ+ Δ − − −
=Δ
+ Δ + Δ − − +=
ΔΔ + Δ
=Δ
= + Δ =
23. ( )
( ) ( ) ( )
( ) ( )
( ) ( )
( ) ( )
( )( )
3
0
3 3
0
2 33 2 3
0
2 32
0
22 2
0
12
lim
12 12lim
3 3 12 12 12lim
3 3 12lim
lim 3 3 12 3 12
Δ →
Δ →
Δ →
Δ →
Δ →
= −
+ Δ −′ =
Δ + Δ − + Δ − − =
Δ+ Δ + Δ + Δ − − Δ − +
=Δ
Δ + Δ + Δ − Δ=
Δ
= + Δ + Δ − = −
x
x
x
x
x
f x x x
f x x f xf x
x
x x x x x x
x
x x x x x x x x x x
x
x x x x x x
x
x x x x x
24. ( )
( ) ( ) ( )
( ) ( )
( ) ( )
( ) ( )
( ) ( )( )
3
0
3 3
0
2 33 3 3
0
2 32
0
22
0
2
4
lim
4 4lim
3 3 4 4 4lim
3 3 4lim
lim 3 3 4
3 4
Δ →
Δ →
Δ →
Δ →
Δ →
= +
+ Δ −′ =
Δ
+ Δ + + Δ − + =Δ
+ Δ + Δ + Δ + + Δ − −=
Δ
Δ + Δ + Δ + Δ=
Δ
= + Δ + Δ +
= +
t
t
t
t
t
g t t t
g t t g tg t
t
t t t t t t
t
t t t t t t t t t t
t
t t t t t t
t
t t t t
t
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Section 2.1 The Derivative and the Tangent Line Problem 117
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25.
( )
( ) ( ) ( )
( ) ( )( )( )
( )( )
( )( )
( )
0
0
0
0
0
2
1
1
lim
1 1
1 1lim
1 1lim
1 1
lim1 1
1lim
1 1
1
1
Δ →
Δ →
Δ →
Δ →
Δ →
=−
+ Δ −′ =
Δ
−+ Δ − −=
Δ− − + Δ −
=Δ + Δ − −
−Δ=Δ + Δ − −
−=+ Δ − −
= −−
x
x
x
x
x
f xx
f x x f xf x
x
x x xx
x x x
x x x x
x
x x x x
x x x
x
26. ( )
( ) ( ) ( )
( )
( )( )
( )( )
( )
2
0
2 2
0
22
2 20
2
20
2 20
4
3
1
lim
1 1
lim
lim
2lim
2lim
2
2
x
x
x
x
x
f xx
f x x f xf x
x
xx x
x
x x x
x x x x
x x x
x x x x
x x
x x x
x
x
x
Δ →
Δ →
Δ →
2Δ →
Δ →
=
+ Δ −′ =
Δ
−+ Δ
=Δ
− + Δ=
Δ + Δ
− Δ − Δ=
Δ + Δ
− − Δ=+ Δ
−=
= −
27. ( )
( ) ( ) ( )
( ) ( )
0
0
0
0
4
lim
4 4 4 4lim
4 4
4 4lim
4 4
1 1 1lim
4 4 4 4 2 4
x
x
x
x
f x x
f x x f xf x
x
x x x x x x
x x x x
x x x
x x x x
x x x x x x
Δ →
Δ →
Δ →
Δ →
= +
+ Δ −′ =
Δ + Δ + − + + Δ + + += ⋅ Δ + Δ + + +
+ Δ + − +=
Δ + Δ + + +
= = =+ Δ + + + + + + +
28. ( )
( ) ( ) ( )
( )
( )
( )( )
0
0
0
0
0
2
lim
2 2lim
2lim
2lim
2lim
2 1
2
s
s
s
s
s
h s s
h s s h sh s
s
s s s
s
s s s s s s
s s s s
s s s
s s s s
s s s
s s
Δ →
Δ →
Δ →
Δ →
Δ →
= −
+ Δ −′ =
Δ
− + Δ − −=
Δ
− + Δ − + Δ += ⋅
Δ + Δ +
− + Δ −=
Δ + Δ +
−=+ Δ +
= − = −
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118 Chapter 2 Differentiation
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29. (a) 2( ) 3f x x= +
( ) ( ) ( )
( ) ( )
( )
( )
( )
0
2 2
0
22 2
0
2
0
0
lim
3 3lim
2 3 3lim
2lim
lim 2 2
Δ →
Δ →
Δ →
Δ →
Δ →
+ Δ −′ =
Δ + Δ + − + =
Δ
+ Δ + Δ + − −=
Δ
Δ + Δ=
Δ= + Δ =
x
x
x
x
x
f x x f xf x
x
x x x
x
x x x x x
x
x x x
x
x x x
At ( )1, 4 ,− the slope of the tangent line is ( )2 1 2.m = − = −
The equation of the tangent line is
( )4 2 1
4 2 2
2 2
y x
y x
y x
− = − +
− = − −= − +
30. (a) 2( ) 2 1f x x x= + −
( ) ( ) ( )
( ) ( )
( )
( )
( )
0
2 2
0
22 2
0
2
0
0
lim
2 1 2 1lim
2 2 2 1 2 1lim
2 2lim
lim 2 2 2 2
Δ →
Δ →
Δ →
Δ →
Δ →
+ Δ −′ =
Δ + Δ + + Δ − − + − =
Δ + Δ + Δ + + Δ − − + − =
Δ
Δ + Δ + Δ=
Δ= + Δ + = +
x
x
x
x
x
f x x f xf x
x
x x x x x x
x
x x x x x x x x
x
x x x x
x
x x x
At ( )1, 2 , the slope of the tangent line is ( )2 1 2 4.m = + =
The equation of the tangent line is
( )2 4 1
2 4 4
4 2.
y x
y x
y x
− = −
− = −= −
(b)
(c) Graphing utility confirms ( )4 at 1, 2 .dy
dx=
(b)
(c) Graphing utility confirms
−3
−1
8
3
(−1, 4)
−10
−4
8
8(1, 2)
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Section 2.1 The Derivative and the Tangent Line Problem 119
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31. (a) ( )
( ) ( ) ( ) ( )
( ) ( )
( ) ( )
( )( )
3
3 3
0 0
2 33 2
0
2 32
0
22 2
0
lim lim
3 3lim
3 3lim
lim 3 3 3
Δ → Δ →
Δ →
Δ →
Δ →
=
+ Δ − + Δ −′ = =
Δ Δ+ Δ + Δ + Δ
=Δ
Δ + Δ + Δ=
Δ
= + Δ + Δ =
x x
x
x
x
f x x
f x x f x x x xf x
x x
x x x x x x
x
x x x x x
x
x x x x x
At ( )2, 8 , the slope of the tangent is ( )23 2 12.m = =
The equation of the tangent line is
( )8 12 2
8 12 24
12 16.
y x
y x
y x
− = −
− = −= −
32. (a) ( )
( ) ( ) ( )
( ) ( )
( ) ( ) ( )
( ) ( )
3
0
3 3
0
2 33 2 3
0
22 2
0
1
lim
1 1lim
3 3 1 1lim
lim 3 3 3
x
x
x
x
f x x
f x x f xf x
x
x x x
x
x x x x x x x
x
x x x x x
Δ →
Δ →
Δ →
Δ →
= +
+ Δ −′ =
Δ + Δ + − + =
Δ
+ Δ + Δ + Δ + − −=
Δ = + Δ + Δ =
At ( )1, 0 ,− the slope of the tangent line is ( )23 1 3.m = − =
The equation of the tangent line is
( )0 3 1
3 3.
y x
y x
− = +
= +
33. (a) ( )
( ) ( ) ( )
( )( )
0
0
0
0
lim
lim
lim
1 1lim
2
Δ →
Δ →
Δ →
Δ →
=
+ Δ −′ =
Δ+ Δ − + Δ += ⋅
Δ + Δ ++ Δ −
=Δ + Δ +
= =+ Δ +
x
x
x
x
f x x
f x x f xf x
x
x x x x x x
x x x x
x x x
x x x x
x x x x
At ( )1, 1 , the slope of the tangent line is 1 1
.22 1
m = =
The equation of the tangent line is
( )11 1
21 1
12 21 1
.2 2
− = −
− = −
= +
y x
y x
y x
(b)
(c) Graphing utility confirms at
(b)
(c) Graphing utility confirms
at
(b)
(c) Graphing utility confirms at
−9
−6
6
9(−1, 0)
5
−1
−1
3
(1, 1)
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120 Chapter 2 Differentiation
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34. (a) ( )
( ) ( ) ( )
( ) ( )( )
0
0
0
0
1
lim
1 1 1 1lim
1 1
1 1lim
1 1
1 1lim
1 1 2 1
x
x
x
x
f x x
f x x f xf x
x
x x x x x x
x x x x
x x x
x x x x
x x x x
Δ →
Δ →
Δ →
Δ →
= −
+ Δ −′ =
Δ + Δ − − − + Δ − + −= ⋅ Δ + Δ − + −
+ Δ − − −=
Δ + Δ − + −
= =+ Δ − + − −
(b)
At ( )5, 2 , the slope of the tangent line is 1 1
.42 5 1
m = =−
The equation of the tangent line is
( )12 5
41 5
24 41 3
.4 4
y x
y x
y x
− = −
− = −
= +
35. (a) ( )
( ) ( ) ( )
( )
( )( ) ( ) ( )( )( )
( ) ( ) ( ) ( )( )( )
( ) ( ) ( )( )( )( )
( )
0
0
2
0
23 2 3 2
0
22
0
2
0
2
2
4
lim
4 4
lim
4 4lim
2 4lim
4lim
4lim
4 41
x
x
x
x
x
x
f x xxf x x f x
f xx
x x xx x x
x
x x x x x x x x x x x
x x x x
x x x x x x x x x
x x x x
x x x x x
x x x x
x x x
x x x
x
x x
Δ →
Δ →
Δ →
Δ →
Δ →
Δ →
= +
+ Δ −′ =
Δ + Δ + − + + Δ =
Δ+ Δ + Δ + − + Δ − + Δ
=Δ + Δ
+ Δ + Δ − − Δ − Δ=
Δ + Δ
Δ + Δ − Δ=
Δ + Δ
+ Δ −=
+ Δ
−= = −2
At ( )4, 5 ,− − the slope of the tangent line is ( )2
4 31 .
44m = − =
−
The equation of the tangent line is
( )35 4
43
5 343
2.4
y x
y x
y x
+ = +
+ = +
= −
(c) Graphing utility confirms
at
(5, 2)
−2
−4
10
4
(b)
(c) Graphing utility confirms
at
−12
−10
6
12
(−4, −5)
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Section 2.1 The Derivative and the Tangent Line Problem 121
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36. (a) ( )
( ) ( ) ( )
( )( ) ( ) ( )( )
( ) ( ) ( )( )
( ) ( ) ( )( )
( )
0
0
2
0
23 2 3 2
0
22 2
0
2 2
0
1
lim
1 1
lim
lim
2lim
2lim
2 1lim
Δ →
Δ →
Δ →
Δ →
Δ →
Δ →
= −
+ Δ −′ =
Δ
+ Δ − − − + Δ =Δ
+ Δ + Δ − − + Δ + + Δ=
Δ + Δ
+ Δ + Δ − − − Δ + + Δ=
Δ + Δ
Δ + Δ − Δ + Δ=
Δ + Δ
+ Δ − +=
x
x
x
x
x
x
f x xx
f x x f xf x
x
x x xx x x
x
x x x x x x x x x x x
x x x x
x x x x x x x x x x x
x x x x
x x x x x x x
x x x x
x x x x
x( )2
2 2
1 11
+ Δ
+= = +
x x
x
x x
At ( )1, 0 , the slope of the tangent line is ( )1 2.m f ′= = The equation of the tangent line is
( )0 2 1
2 2.
y x
y x
− = −
= −
37. Using the limit definition of a derivative, ( ) 1.
2f x x′ = −
Because the slope of the given line is 1,− you have
1
12
2.
x
x
− = −
=
At the point ( )2, 1 ,− the tangent line is parallel to
0.x y+ = The equation of this line is
( ) ( )1 1 2
1.
y x
y x
− − = − −
= − +
38. Using the limit definition of derivative, ( ) 4 .f x x′ =
Because the slope of the given line is –4, you have
4 4
1.
x
x
= −= −
At the point ( )1, 2− the tangent line is parallel to
4 3 0.x y+ + = The equation of this line is
( )2 4 1
4 2.
y x
y x
− = − +
= − −
39. From Exercise 31 we know that ( ) 23 .f x x′ =
Because the slope of the given line is 3, you have
23 3
1.
x
x
== ±
Therefore, at the points ( )1, 1 and ( )1, 1− − the tangent
lines are parallel to 3 1 0.x y− + =
These lines have equations
( ) ( )1 3 1 and 1 3 1
3 2 3 2.
y x y x
y x y x
− = − + = += − = +
40. Using the limit definition of derivative, ( ) 23 .f x x′ =
Because the slope of the given line is 3, you have
2
2
3 3
1 1.
x
x x
=
= = ±
Therefore, at the points ( )1, 3 and ( )1, 1− the tangent
lines are parallel to 3 4 0.x y− − = These lines have
equations
( ) ( )3 3 1 and 1 3 1
3 3 4.
y x y x
y x y x
− = − − = += = +
(b)
(c) Graphing utility confirms
at
−5
4
−4
5(1, 0)
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122 Chapter 2 Differentiation
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41. Using the limit definition of derivative,
( ) 1.
2f x
x x
−′ =
Because the slope of the given line is 1
,2
− you have
1 1
22
1.
x x
x
− = −
=
Therefore, at the point ( )1, 1 the tangent line is parallel to
2 6 0.x y+ − = The equation of this line is
( )11 1
21 1
12 21 3
.2 2
− = − −
− = − +
= − +
y x
y x
y x
42. Using the limit definition of derivative,
( )( )3 2
1.
2 1f x
x
−′ =−
Because the slope of the given line is 1
,2
− you have
( )
( )
3 2
3 2
1 1
22 1
1 1
1 1 2.
x
x
x x
− = −−
= −
= − =
At the point ( )2, 1 , the tangent line is parallel to
2 7 0.x y+ + = The equation of the tangent line is
( )11 2
21
2.2
− = − −
= − +
y x
y x
43. The slope of the graph of f is 1 for all x-values.
44. The slope of the graph of f is 0 for all x-values.
45. The slope of the graph of f is negative for 4,x <positive for 4,x > and 0 at 4.x =
46. The slope of the graph of f is –1 for 4,x < 1 for
4,x > and undefined at 4.x =
47. The slope of the graph of f is negative for 0x < and positive for 0.x > The slope is undefined at 0.x =
48. The slope is positive for 2 0x− < < and negative for 0 2.x< < The slope is undefined at 2,x = ± and 0 at
0.x =
2
−2
−1
3
4
1 2−2 −1 3−3
f ′
y
x
−1−2 1 2
−1
−2
1
2
x
y
f ′
−2−4−6 2 4 6−2
−4
−6
−8
2
4
x
y
f ′
x
y
f ′
1 2 3 4 5 6
1
2
3
y
x−1−2 1 2 3 4
−2
1
2
f ′
−1−2 1 2
−1
−2
1
2f ′
y
x
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Section 2.1 The Derivative and the Tangent Line Problem 123
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49. Answers will vary.
Sample answer: y x= −
The derivative of = −y x is 1.y′ = − So, the derivative
is always negative.
50. Answers will vary. Sample answer: 3 23y x x= −
Note that ( )23 6 3 2 .y x x x x′ = − = −
So, 0y′ = at 0x = and 2.x =
51. No. For example, the domain of ( )f x x= is 0,x ≥
whereas the domain of ( ) 1
2f x
x′ = is 0.x >
52. No. For example, ( ) 3f x x= is symmetric with respect to
the origin, but its derivative, ( ) 23 ,f x x′ = is symmetric
with respect to the -axis.y
53. ( )4 5g = because the tangent line passes through ( )4, 5 .
( ) 5 0 54
4 7 3g
−′ = = −−
54. ( )1 4h − = because the tangent line passes through
( )1, 4 .−
( ) ( )6 4 2 1
13 1 4 2
h−′ − = = =
− −
55. ( ) 5 3f x x= − and 1c =
56. ( ) 3f x x= and 2c = −
57. ( ) 2f x x= − and 6c =
58. ( ) 2f x x= and 9c =
59. ( )0 2f = and ( ) 3,f x x′ = − −∞ < < ∞
( ) 3 2f x x= − +
60. ( ) ( ) ( )0 4, 0 0; 0f f f x′ ′= = < for ( )0, 0x f x′< >
for 0x >
Answers will vary: Sample answer: ( ) 2 4f x x= +
61. Let ( )0 0,x y be a point of tangency on the graph of f.
By the limit definition for the derivative,
( ) 4 2 .f x x′ = − The slope of the line through ( )2, 5 and
( )0 0,x y equals the derivative of f at 0 :x
( )( )( )
( )( )
00
0
0 0 0
2 20 0 0 0
20 0
0 0 0
54 2
2
5 2 4 2
5 4 8 8 2
0 4 3
0 1 3 1, 3
yx
x
y x x
x x x x
x x
x x x
− = −−− = − −
− − = − +
= − += − − =
Therefore, the points of tangency are ( )1, 3 and ( )3, 3 ,
and the corresponding slopes are 2 and –2. The equations of the tangent lines are:
( ) ( )5 2 2 5 2 2
2 1 2 9
y x y x
y x y x
− = − − = − −= + = − +
x
−1
−2
−3
−4
2
1
3
4
−2 −1−3−4 2 3 4
y
−1−2 1 2
−3
−4
1
x
y
−1−2−3 2 3−1
−2
−3
x
y
f
1
2
−2−4−6 2 4 6
2
4
6
8
10
12
x
y
f
x1 2 3 6−2
2
4
3
5
7
6
1
(1, 3)(3, 3)
(2, 5)
y
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124 Chapter 2 Differentiation
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62. Let ( )0 0,x y be a point of tangency on the graph of f.
By the limit definition for the derivative, ( ) 2 .f x x′ =
The slope of the line through ( )1, 3− and ( )0 0,x y equals
the derivative of f at 0 :x
( )
( )( )
00
0
0 0 0
2 20 0 0
20 0
0 0 0
32
1
3 1 2
3 2 2
2 3 0
3 1 0 3, 1
yx
x
y x x
x x x
x x
x x x
− − =−
− − = −
− − = −− − =
− + = = −
Therefore, the points of tangency are ( )3, 9 and ( )1, 1 ,−
and the corresponding slopes are 6 and –2. The equations of the tangent lines are:
( ) ( )3 6 1 3 2 1
6 9 2 1
y x y x
y x y x
+ = − + = − −= − = − −
63. (a) ( )
( ) ( ) ( )
( )
( ) ( )
( )
( )
2
0
2 2
0
22 2
0
0
0
lim
lim
2lim
2lim
lim 2 2
Δ →
Δ →
Δ →
Δ →
Δ →
=
+ Δ −′ =
Δ+ Δ −
=Δ
+ Δ + Δ −=
ΔΔ + Δ
=Δ
= + Δ =
x
x
x
x
x
f x x
f x x f xf x
x
x x x
x
x x x x x
xx x x
xx x x
At ( )1, 1 2x f ′= − − = − and the tangent line is
( )1 2 1 or 2 1.y x y x− = − + = − −
At ( )0, 0 0x f ′= = and the tangent line is 0.y =
At ( )1, 1 2x f ′= = and the tangent line is
2 1.y x= −
For this function, the slopes of the tangent lines are always distinct for different values of x.
(b) ( ) ( ) ( )
( )
( ) ( ) ( )
( ) ( )( )
( ) ( )( )
0
3 3
0
2 33 2 3
0
22
0
22 2
0
lim
lim
3 3lim
3 3lim
lim 3 3 3
x
x
x
x
x
g x x g xg x
x
x x x
x
x x x x x x x
x
x x x x x
x
x x x x x
Δ →
Δ →
Δ →
Δ →
Δ →
+ Δ −′ =Δ
+ Δ −=
Δ
+ Δ + Δ + Δ −=
Δ
Δ + Δ + Δ=
Δ
= + Δ + Δ =
At ( )1, 1 3x g′= − − = and the tangent line is
( )1 3 1 or 3 2.y x y x+ = + = +
At ( )0, 0 0x g′= = and the tangent line is 0.y =
At ( )1, 1 3x g′= = and the tangent line is
( )1 3 1 or 3 2.y x y x− = − = −
For this function, the slopes of the tangent lines are sometimes the same.
64. (a) ( )0 3g′ = −
(b) ( )3 0g′ =
(c) Because ( ) 83
1 ,g g′ = − is decreasing (falling) at
1.x =
(d) Because ( ) 73
4 ,g g′ − = is increasing (rising) at
4.x = −
(e) Because ( )4g′ and ( )6g′ are both positive, ( )6g is
greater than ( )4 ,g and ( ) ( )6 4 0.g g− >
(f) No, it is not possible. All you can say is that g is decreasing (falling) at 2.x =
x2 4 6−2−6 −4−8
−2
−4
4
8
6
10(3, 9)
(1, −3)
(−1, 1)
y
−3
−3
3
2
−3 3
−2
2
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Section 2.1 The Derivative and the Tangent Line Problem 125
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65. ( ) 21
2f x x=
(a)
( ) ( ) ( ) ( )0 0, 1 2 1 2, 1 1, 2 2f f f f′ ′ ′ ′= = = =
(b) By symmetry: ( ) ( ) ( )1 2 1 2, 1 1, 2 2f f f′ ′ ′− = − − = − − = −
(c)
(d) ( ) ( ) ( ) ( ) ( ) ( )( )2 22 2 2
0 0 0 0
1 1 1 12
2 2 2 2lim lim lim lim2x x x x
x x x x x x x xf x x f x xf x x x
x x xΔ → Δ → Δ → Δ →
+ Δ − + Δ + Δ −+ Δ − Δ ′ = = = = + = Δ Δ Δ
66. ( ) 31
3f x x=
(a)
( ) ( ) ( ) ( )0 0, 1 2 1 4, 1 1, 2 4,f f f f′ ′ ′ ′= = = = ( )3 9f ′ =
(b) By symmetry: ( ) ( )1 2 1 4, 1 1,f f′ ′− = − = ( ) ( )2 4, 3 9f f′ ′− = − =
(c)
(d) ( ) ( ) ( )
( )
( ) ( ) ( )( )
( ) ( )
0
3 3
0
2 33 2 3
0
22 2
0
lim
1 1
3 3lim
1 13 3
3 3lim
1lim
3
x
x
x
x
f x x f xf x
x
x x x
x
x x x x x x x
x
x x x x x
Δ →
Δ →
Δ →
Δ →
+ Δ −′ =
Δ
+ Δ −=
Δ
+ Δ + Δ + Δ −=
Δ = + Δ + Δ =
−2
−6 6
6
y
x−2−3−4 1 2 3 4
−2
−3
−4
1
2
3
4
f ′
−9
−6
9
6
−1−2−3 1 2 3−1
1
2
3
4
5
x
y
f ′
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126 Chapter 2 Differentiation
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67. ( ) ( ) ( ) ( )
( ) ( )
2 2 4 2 4, 2.1 2.1 4 2.1 3.99
3.99 42 0.1 Exact: 2 0
2.1 2
f f
f f
= − = = − =
−′ ′≈ = − = −
68. ( ) ( ) ( )
( ) ( )
312 2 2, 2.1 2.31525
42.31525 2
2 3.1525 Exact: 2 32.1 2
f f
f f
= = =
−′ ′≈ = = −
69. ( ) 3 22 1, 2f x x x c= + + = −
( ) ( ) ( )
( )
( )
2
3 2
2
22
2 2
22 lim
2
2 1 1lim
2
2lim lim 4
2
x
x
x x
f x ff
x
x x
x
x xx
x
→−
→−
→− →−
− −′ − =+
+ + −=
++
= = =+
70. ( ) 2 , 1g x x x c= − =
( ) ( ) ( )
( )
1
2
1
1
1
11 lim
1
0lim
1
1lim
1lim 1
x
x
x
x
g x gg
x
x x
x
x x
xx
→
→
→
→
−′ =−
− −=−
−=
−= =
71. ( ) , 0g x x c= =
( ) ( ) ( )0 0
00 lim lim .
0x x
xg x gg
x x→ →
−′ = =
−Does not exist.
As 1
0 , .x
xx x
− −→ = → −∞
As 1
0 , .x
xx x
+→ = → ∞
Therefore ( )g x is not differentiable at 0.x =
72. ( ) 3, 4f x c
x= =
( ) ( ) ( )
( )( )( )
4
4
4
4
4
3 34
44 lim
4
lim4
12 3lim
4 4
3 4lim
4 4
3 3lim
4 16
x
x
x
x
x
x
f x ff
x
xx
x x
x
x x
x
→
→
→
→
→
−′ =
−−
=−
−=−
− −=
−
= − = −
73. ( ) ( )2 36 , 6f x x c= − =
( ) ( ) ( )
( )( )
6
2 3
1 36 6
66 lim
6
6 0 1lim lim .
6 6
x
x x
f x ff
x
x
x x
→
→ →
−′ =−
− −= =
− −
Does not exist.
Therefore ( )f x is not differentiable at 6.x =
74. ( ) ( )1 33 , 3g x x c= + = −
( ) ( ) ( )( )
( )( )
3
1 3
2 33 3
33 lim
3
3 0 1lim lim .
3 3
x
x x
g x gg
x
x
x x
→−
→− →−
− −′ − =− −
+ −= =
+ +
Does not exist.
Therefore ( )g x is not differentiable at 3.x = −
75. ( ) 7 , 7h x x c= + = −
( ) ( ) ( )( )7
7 7
77 lim
7
7 0 7lim lim .
7 7
x
x x
h x hh
x
x x
x x
→−
→− →−
− −′ − =− −
+ − += =
+ +
Does not exist.
Therefore ( )h x is not differentiable at 7.x = −
76. ( ) 6 , 6f x x c= − =
( ) ( ) ( )6
6 6
66 lim
6
6 0 6lim lim .
6 6
x
x x
f x ff
x
x x
x x
→
→ →
−′ =−
− − −= =
− −
Does not exist.
Therefore ( )f x is not differentiable at 6.x =
77. ( )f x is differentiable everywhere except at 4.x = −
(Sharp turn in the graph)
78. ( )f x is differentiable everywhere except at 2.x = ±
(Discontinuities)
79. ( )f x is differentiable on the interval ( )1, .− ∞ (At
1= −x the tangent line is vertical.)
80. ( )f x is differentiable everywhere except at 0.x =
(Discontinuity)
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Section 2.1 The Derivative and the Tangent Line Problem 127
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81. ( ) 5f x x= − is differentiable
everywhere except at 5.=x There is a sharp corner at
5.x =
82. ( ) 4
3
xf x
x=
−is differentiable
everywhere except at 3.x = f is not defined at 3.x = (Vertical asymptote)
83. ( ) 2 5f x x= is differentiable
for all 0.x ≠ There is a sharp corner at 0.x =
84. f is differentiable for all 1.x ≠
f is not continuous at 1.x =
85. ( ) 1f x x= −
The derivative from the left is
( ) ( )
1 1
1 01lim lim 1.
1 1x x
xf x f
x x− −→ →
− −−= = −
− −
The derivative from the right is
( ) ( )
1 1
1 01lim lim 1.
1 1x x
xf x f
x x+ +→ →
− −−= =
− −
The one-sided limits are not equal. Therefore, f is not differentiable at 1.x =
86. ( ) 21f x x= −
The derivative from the left does not exist because
( ) ( ) 2
1 1
2 2
21
21
1 1 0lim lim
1 1
1 1lim
1 1
1lim .
1
x x
x
x
f x f x
x x
x x
x x
x
x
− −→ →
−→
−→
− − −=− −
− −= ⋅− −+= − = −∞−
(Vertical tangent)
The limit from the right does not exist since f is undefined for 1.x > Therefore, f is not differentiable at
1.x =
87. ( ) ( )( )
3
2
1 , 1
1 , 1
x xf x
x x
− ≤= − >
The derivative from the left is
( ) ( ) ( )
( )
3
1 1
2
1
1 1 0lim lim
1 1
lim 1 0.
x x
x
f x f x
x x
x
− −→ →
−→
− − −=
− −
= − =
The derivative from the right is
( ) ( ) ( )
( )
2
1 1
1
1 1 0lim lim
1 1
lim 1 0.
x x
x
f x f x
x x
x
+ +→ →
+→
− − −=
− −= − =
The one-sided limits are equal. Therefore, f is
differentiable at 1.x = ( )( )1 0f ′ =
88. ( ) ( )2 31f x x= −
The derivative from the left does not exist.
( ) ( ) ( )
( )
2 3
1 1
1 31
1 1 0lim lim
1 1
1lim
1
− −→ →
−→
− − −=
− −−= = −∞
−
x x
x
f x f x
x x
x
Similarly, the derivative from the right does not exist because the limit is .∞
Therefore, f is not differentiable at 1.x =
89. Note that f is continuous at 2.x =
( )2 1, 2
4 3, 2
x xf x
x x
+ ≤= − >
The derivative from the left is
( ) ( ) ( )
( )
2
2 2
2
1 52lim lim
2 2
lim 2 4.
x x
x
xf x f
x x
x
− −→ →
−→
+ −−=
− −= + =
The derivative from the right is
( ) ( ) ( )
2 2 2
2 4 3 5lim lim lim 4 4.
2 2x x x
f x f x
x x+ + +→ → →
− − −= = =
− −
The one-sided limits are equal. Therefore, f is
differentiable at 2.x = ( )( )2 4f ′ =
90. ( )12
2, 2
2 , 2
x xf x
x x
+ <= ≥
f is not differentiable at 2=x because it is not
continuous at 2.x =
( ) ( )
( ) ( )2
2
1lim 2 2 3
2
lim 2 2 2
x
x
f x
f x
−→
+→
= + =
= =
−1
−1 11
7
−8
−6
12
15
6
−3
−6
5
3
5
−3
−4
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128 Chapter 2 Differentiation
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91. (a) The distance from ( )3, 1 to the line 4 0mx y− + = is ( ) ( )1 1
2 2 2 2
3 1 1 4 3 3.
1 1
mAx By C md
A B m m
− ++ + += = =
+ + +
(b)
The function d is not differentiable at 1.m = − This corresponds to the line 4,y x= − + which passes through
the point ( )3, 1 .
92. (a) ( ) 2f x x= and ( ) 2f x x′ = (b) ( ) 3g x x= and ( ) 23g x x′ =
(c) The derivative is a polynomial of degree 1 less than the original function. If ( ) ,nh x x= then ( ) 1.nh x nx −′ =
(d) If ( ) 4,f x x= then
( ) ( ) ( )
( )
( ) ( ) ( ) ( )
( ) ( ) ( )( )( ) ( ) ( )( )
0
4 4
0
2 3 44 3 2 4
0
2 33 22 33 2 3
0 0
lim
lim
4 6 4lim
4 6 4lim lim 4 6 4 4 .
x
x
x
x x
f x x f xf x
x
x x x
x
x x x x x x x x x
x
x x x x x x xx x x x x x x
x
Δ →
Δ →
Δ →
Δ → Δ →
+ Δ −′ =Δ
+ Δ −=
Δ
+ Δ + Δ + Δ + Δ −=
Δ
Δ + Δ + Δ + Δ= = + Δ + Δ + Δ =
Δ
So, if ( ) 4,f x x= then ( ) 34f x x′ = which is consistent with the conjecture. However, this is not a proof because you
must verify the conjecture for all integer values of , 2.n n ≥
93. False. The slope is ( ) ( )
0
2 2lim .x
f x f
xΔ →
+ Δ −Δ
94. False. 2y x= − is continuous at 2,x = but is not
differentiable at 2.x = (Sharp turn in the graph)
95. False. If the derivative from the left of a point does not equal the derivative from the right of a point, then the derivative does not exist at that point. For example, if
( ) ,f x x= then the derivative from the left at 0x = is
–1 and the derivative from the right at 0x = is 1. At 0,x = the derivative does not exist.
96. True. See Theorem 2.1.
x
2
3
1 2 3 4
1
y
5
−1
−4 4
x1 2 3 4−1−3 −2−4
1
3
2
f
f '
4
5
−3
y
g
g′
x−2 −1
1
3
2
1 2
−1
y
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Section 2.2 Basic Differentiation Rules and Rates of Change 129
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97. ( ) ( )sin 1 , 0
0, 0
x x xf x
x
≠= =
Using the Squeeze Theorem, you have ( )sin 1 , 0.x x x x x− ≤ ≤ ≠ So, ( ) ( )0
lim sin 1 0 0x
x x f→
= = and
f is continuous at 0.x = Using the alternative form of the derivative, you have
( ) ( ) ( )
0 0 0
0 sin 1 0 1lim lim lim sin .
0 0x x x
f x f x x
x x x→ → →
− − = = − −
Because this limit does not exist ( ( )sin 1 x oscillates between –1 and 1), the function is not differentiable at 0.x =
( ) ( )2 sin 1 , 0
0, 0
x x xg x
x
≠= =
Using the Squeeze Theorem again, you have ( )2 2 2sin 1 , 0.x x x x x− ≤ ≤ ≠ So, ( ) ( )2
0lim sin 1 0 0x
x x g→
= =
and g is continuous at 0.x = Using the alternative form of the derivative again, you have
( ) ( ) ( )2
0 0 0
0 sin 1 0 1lim lim lim sin 0.
0 0x x x
g x g x xx
x x x→ → →
− −= = =
− −
Therefore, g is differentiable at ( )0, 0 0.x g′= =
98.
As you zoom in, the graph of 21 1y x= + appears to be locally the graph of a horizontal line, whereas the graph of
2 1y x= + always has a sharp corner at ( ) 20, 1 . y is not differentiable at ( )0, 1 .
Section 2.2 Basic Differentiation Rules and Rates of Change
1. The derivative of a constant function is 0.
[ ] 0d
cdx
=
2. To find the derivative of ( ) ,nf x cx= multiply n by ,c
and reduce the power of x by 1.
( ) 1−′ = nf x ncx
3. The derivative of the sine function, ( ) sin ,f x x= is the
cosine function, ( ) cos .f x x′ =
The derivative of the cosine function, ( ) cos ,g x x= is
the negative of the sine function, ( ) sin .g x x′ = −
4. The average velocity of an object is the change in distance divided by the change in time. The velocity is the instantaneous change in velocity. It is the derivative of the position function.
5. (a)
( )
1 2
1 212
12
1
y x
y x
y
−
=
′ =
′ =
(b)
( )
3
23
1 3
y x
y x
y
=
′ =′ =
6. (a)
( )
1 2
3 212
12
1
y x
y x
y
−
−
=
′ = −
′ = −
(b)
( )
1
2
1 1
y x
y x
y
−
−
=
′ = −′ = −
−3 3
−1
3
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130 Chapter 2 Differentiation
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7. 12
0
=′ =
y
y
8. ( )( )
9
0
f x
f x
= −
′ =
9. 7
67
y x
y x
=
′ =
10. 12
1112
y x
y x
=
′ =
11. 55
66
1
55
y xx
y xx
−
−
= =
′ = − = −
12.
( )
77
88
33
213 7
y xx
y xx
−
−
= =
′ = − = −
13. ( )
( )
9 1 9
8 98 9
1 1
9 9
f x x x
f x xx
−
= =
′ = =
14. 4 1 4
3 43 4
1 1
4 4
y x x
y xx
−
= =
′ = =
15. ( )( )
11
1
f x x
f x
= +
′ =
16. ( )( )
6 3
6
g x x
g x
= +
′ =
17. ( )( )
23 2 6
6 2
f t t t
f t t
= − + −
′ = − +
18. 2 3 1
2 3
y t t
y t
= − +′ = −
19. ( )( )
2 3
2
4
2 12
g x x x
g x x x
= +
′ = +
20. 3
2
4 3
4 9
y x x
y x
= −
′ = −
21. ( )( )
3 2
2
5 3 8
3 10 3
s t t t t
s t t t
= + − +
′ = + −
22. 3 2
2
2 6 1
6 12
y x x
y x x
= + −
′ = +
23. sin2
cos2
y
y
π θ
π θ
=
′ =
24. ( )( )
cos
sin
g t t
g t t
π
π
=
′ = −
25. 2 12
12
cos
2 sin
y x x
y x x
= −
′ = +
26.
( )4
3 3
7 2 sin
7 4 2 cos 28 2 cos
y x x
y x x x x
= +
′ = + = +
Function Rewrite Differentiate Simplify
27. 4 54 5
2 2 8 8
7 7 7 7− −′ ′= = = − = −y y x y x y
x x
28. ( )5 4 45
8 8 85 8
5 5 5−′ ′= = = =y y x y x y x
x
29. ( )
3 43 4
6 6 18 18
125 125 1255y y x y x y
xx− −′ ′= = = − = −
30. ( )
( )22
312 12 2 24
2− ′ ′= = = =y y x y x y x
x
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Section 2.2 Basic Differentiation Rules and Rates of Change 131
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31. ( ) ( )
( )
( )
22
33
88 , 2, 2
1616
2 2
f x xx
f x xx
f
−
−
= =
′ = − = −
′ = −
32. ( ) ( )
( )
( )
1
22
42 2 4 , 4, 1
44
14
4
f t tt
f t tt
f
−
−
= − = −
′ = =
′ =
33. ( ) ( )( )( )
3
2
71 12 5 2
215
, 0,
0 0
f x x
f x x
f
= − + −
′ =
′ =
34. ( )
( )
4
3
2 3, 1, 1
8
1 8
y x
y x
y
= − −
′ =′ =
35. ( ) ( )
( ) ( )
2
2
4 1 , 0, 1
16 8 1
32 8
0 32 0 8 8
= +
= + +′ = +
′ = + =
y x
x x
y x
y
36. ( ) ( ) ( )
( )( )
2
2
2 4 , 2, 8
2 16 32
4 16
2 8 16 8
f x x
x x
f x x
f
= −
= − +′ = −
′ = − = −
37. ( ) ( )( )( ) ( )
4 sin , 0, 0
4 cos 1
0 4 1 1 3
f
f
f
θ θ θ
θ θ
= −
′ = −
′ = − =
38. ( ) ( )( )
( )
2 cos 5, , 7
2 sin
0
g t t
g t t
g
π
π
= − +
′ =
′ =
39. ( )
( )
2 2
33
5 3
62 6 2
f x x x
f x x x xx
−
−
= + −
′ = + = +
40. ( )
( )
3 3
2 4 24
2 3
93 2 9 3 2
f x x x x
f x x x xx
−
−
= − +
′ = − − = − −
41. ( )
( )
2 2 33
44
44
122 12 2
g t t t tt
g t t t tt
−
−
= − = −
′ = + = +
42. ( )
( )
22
33
38 8 3
68 6 8
f x x x xx
f x xx
−
−
= + = +
′ = − = −
43. ( )
( )
3 22
2
3
3 3
3 43 4
8 81
x xf x x x
x
xf x
x x
−− += = − +
−′ = − =
44. ( )
( )
32 1
22
4 2 54 2 5
58 5 8
x xh x x x
x
h x x x xx
−
−
+ += = + +
′ = − = −
45. ( )
( )
21 2 1 2 3 2
3 2
1 2 3 2 5 2
2
5 2
3 4 83 4 8
32 12
2
3 4 24
2
t tg t t t t
t
g t t t t
t t
t
− −
− − −
+ −= = + −
′ = − +
− +=
46. ( )
( )
514 3 2 3 1 3
1 3
11 3 1 3 4 3
5
4 3
2 62 6
14 42
3 3
14 4 6
3
s sh s s s s
s
h s s s s
s s
s
−
− −
+ += = + +
′ = + −
+ −=
47. ( )2 3
2
1
3 1
y x x x x
y x
= + = +
′ = +
48. ( )( )
2 2 4 3
3 2 2
2 3 2 3
8 9 8 9
y x x x x x
y x x x x
= − = −
′ = − = −
49. ( )
( )
3 1 2 1 3
1 2 2 32 3
6 6
1 1 22
2 2
f x x x x x
f x x xxx
− −
= − = −
′ = − = −
50. ( )
( )
2 3 1 3
1 3 2 31 3 2 3
4
2 1 2 1
3 3 3 3
f t t t
f t t tt t
− −
= − +
′ = − = −
51. ( )
( )
1 2
1 2
6 5 cos 6 5 cos
33 5 sin 5 sin
f x x x x x
f x x x xx
−
= + = +
′ = − = −
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132 Chapter 2 Differentiation
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52. ( )
( )
1 33
4 34 3
23 cos 2 3 cos
2 23 sin 3 sin
3 3
f x x x xx
f x x x xx
−
−
= + = +
′ = − − = − −
53. ( )
( )2 22
15 cos 3 5 cos 9 5 cos
3
18 5 sin
−= − = − = −
′ = +
y x x x x xx
y x x
54. ( )
33
4
4
3 32 sin 2 sin
82
92 cos
89
2 cos8
y x x xx
y x x
xx
−
−
= + = +
−′ = +
= − +
55. (a) ( )( )
4 2
3
2 5 3
8 10
f x x x
f x x x
= − + −
′ = − +
At ( ) ( ) ( ) ( )31, 0 : 1 8 1 10 1 2f ′ = − + =
Tangent line: ( )0 2 1
2 2
y x
y x
− = −
= −
(b) and (c)
56. (a) 3
2
3
3 3
y x x
y x
= −
′ = −
At ( ) ( )22, 2 : 3 2 3 9y′ = − =
Tangent line: ( )2 9 2
9 16
9 16 0
y x
y x
x y
− = −
= −− − =
(b) and (c)
57. (a) ( )
( )
3 4
4 3
7 47 4
22
3 3
2 2
f x xx
f x xx
−
−
= =
′ = − = −
At ( ) ( ) 31, 2 : 1
2f ′ = −
Tangent line: ( )32 1
23 7
2 23 2 7 0
y x
y x
x y
− = − −
= − +
+ − =
(b) and (c)
58. (a) ( )( )2 3 2
2
2 3 6
3 2 6
y x x x x x x
y x x
= − + = + −
′ = + −
At ( ) ( ) ( )21, 4 : 3 1 2 1 6 1y′− = + − = −
Tangent line: ( ) ( )4 1 1
3
3 0
y x
y x
x y
− − = − −
= − −+ + =
(b) and (c)
59.
( )( )( )
4 2
3
2
2 3
4 4
4 1
4 1 1
0 0, 1
y x x
y x x
x x
x x x
y x
= − +
′ = −
= −
= − +
′ = = ±
Horizontal tangents: ( ) ( ) ( )0, 3 , 1, 2 , 1, 2−
60. 3
23 1 0 for all .
y x x
y x x
= +
′ = + >
Therefore, there are no horizontal tangents.
61. 22
33
1
22 cannot equal zero.
y xx
y xx
−
−
= =
′ = − = −
Therefore, there are no horizontal tangents.
−3
−3 3
1
(1, 0)
−4
−3
3
5
(2, 2)
7
−1
−2
5
(1, 2)
−10
−5 5
(1, −4)
10
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Section 2.2 Basic Differentiation Rules and Rates of Change 133
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62. 2 9
2 0 0
y x
y x x
= +′ = = =
At 0, 1.x y= =
Horizontal tangent: ( )0, 9
63. sin , 0 2
1 cos 0
cos 1
y x x x
y x
x x
π
π
= + ≤ <′ = + =
= − =
At :x yπ π= =
Horizontal tangent: ( ),π π
64. 3 2 cos , 0 2
3 2 sin 0
3 2sin or
2 3 3
y x x x
y x
x x
π
π π
= + ≤ <
′ = − =
= =
At 3 3
:3 3
x yπ π += =
At 2 2 3 3
:3 3
x yπ π −= =
Horizontal tangents: 3 3 2 2 3 3
, , ,3 3 3 3
π π π π + −
65. ( ) 2, 6 1f x k x y x= − = − +
( ) 2f x x′ = − and slope of tangent line is 6.m = −
( ) 6
2 6
3
f x
x
x
′ = −
− = −=
( )2
6 3 1 17
17 3
8
y
k
k
= − + = −
− = −=
66. ( ) 2, 2 3f x kx y x= = − +
( ) 2f x kx′ = and slope of tangent line is 2.m = −
( ) 2
2 2
1
f x
kx
xk
′ = −
= −
= −
1 2
2 3 3yk k
= − − + = +
2
2 13
2 13
13
1
3
kk k
k k
k
k
+ = −
+ =
= −
= −
67. ( ) 3, 3
4
kf x y x
x= = − +
( ) 2
kf x
x′ = − and slope of tangent line is
3.
4m = −
( )
2
2
3
43
44
3
4
3
f x
k
xk
x
kx
′ = −
− = −
=
=
3 3 4
3 34 4 3
ky x= − + = − +
3 4 3
34 3 4
3
kk
k
k
− + =
=
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134 Chapter 2 Differentiation
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68. ( ) , 4f x k x y x= = +
( )2
kf x
x′ = and slope of tangent line is 1.m =
( )
2
1
12
2
4
′ =
=
=
=
f x
k
xk
x
kx
2
4 44
ky x= + = +
2
2 2
2
2
44 2
44 2
44
16
4
+ = ⋅
− = −
− = −
==
k kk
k k
k
k
k
69. ( ) ( ) ( ) ( )6g x f x g x f x′ ′= + =
70. ( ) ( ) ( ) ( )2 2g x f x g x f x′ ′= =
71. ( ) ( ) ( ) ( )5 5g x f x g x f x′ ′= − = −
72. ( ) ( ) ( ) ( )3 1 3g x f x g x f x′ ′= − =
73.
If f is linear then its derivative is a constant function.
( )( )
f x ax b
f x a
= +
′ =
74.
If f is quadratic, then its derivative is a linear function.
( )( )
2
2
f x ax bx c
f x ax b
= + +
′ = +
75. The graph of a function f such that 0f ′ > for all x and
the rate of change of the function is decreasing (i.e., as x increases, ′f decreases) would, in general, look
like the graph below.
76. (a) The slope appears to be steepest between A and B.
(b) The average rate of change between A and B is greater than the instantaneous rate of change at B.
(c)
3
3
1
21−1−2−3
−2
x
f
f ′
y
x−2 −1 1 3 4
1
2
−3
−4
f
f ′
y
x
y
x
f
CA
B
ED
y
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Section 2.2 Basic Differentiation Rules and Rates of Change 135
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77. Let ( )1 1,x y and ( )2 2,x y be the points of tangency on 2y x= and 2 6 5,y x x= − + − respectively.
The derivatives of these functions are:
1 2
1 2
1 2
2 2 and 2 6 2 6
2 2 6
3
y x m x y x m x
m x x
x x
′ ′= = = − + = − += = − +
= − +
Because 21 1y x= and 2
2 2 26 5:y x x= − + −
( ) ( )2 2
2 2 12 12
2 1 2 1
6 52 6
x x xy ym x
x x x x
− + − −−= = = − +− −
( ) ( )
( )( ) ( ) ( )( )
( )( )
222 2 2
22 2
2 22 2 2 2 2 2
2 22 2 2 2
22 2
2 2
2
6 5 32 6
3
6 5 6 9 2 6 2 3
2 12 14 4 18 18
2 6 4 0
2 2 1 0
1 or 2
x x xx
x x
x x x x x x
x x x x
x x
x x
x
− + − − − += − +
− − +
− + − − − + = − + −
− + − = − + −
− + =
− − =
=
2 2 11 0, 2x y x= = = and 1 4y =
So, the tangent line through ( )1, 0 and ( )2, 4 is So, the tangent line through ( )2, 3 and ( )1, 1 is
( )4 00 1 4 4.
2 1y x y x
− − = − = − − ( )3 1
1 1 2 1.2 1
y x y x− − = − = − −
2 2 12 3, 1x y x= = = and 1 1y =
78. 1m is the slope of the line tangent to 2.y x m= is the slope of the line tangent to 1 .y x= Because
1 22 2
1 1 11 1 and .y x y m y y m
x x x′ ′= = = = = − = −
The points of intersection of y x= and 1y x= are
211 1.x x x
x= = = ±
At 21, 1.x m= ± = − Because 2 11 ,m m= − these tangent lines are perpendicular at the points of intersection.
79. ( )( )
3 sin 2
3 cos
f x x x
f x x
= + +
′ = +
Because ( )cos 1, 0x f x′≤ ≠ for all x and f does not
have a horizontal tangent line.
80. ( )( )
5 3
4 2
3 5
5 9 5
f x x x x
f x x x
= + +
′ = + +
Because ( )4 25 9 0, 5.x x f x′+ ≥ ≥ So, f does not
have a tangent line with a slope of 3.
5
4
3
1
−1
−2
2
2 3x
(1, 0)
(2, 4)
y
5
4
3
1
−1
2
2 3x
(2, 3)
(1, 1)
y
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136 Chapter 2 Differentiation
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81. ( ) ( )
( ) 1 2
, 4, 0
1 1
2 2
1 0
42
4 2
4 2
4 2
4, 2
f x x
f x xx
y
xx
x x y
x x x
x x
x y
−
= −
′ = =
−=− −
+ =
+ =+ =
= =
The point ( )4, 2 is on the graph of f.
Tangent line: ( )0 22 4
4 44 8 4
0 4 4
y x
y x
x y
−− = −− −
− = −= − +
82. ( ) ( )
( ) 2
2, 5, 0
2
f xx
f xx
=
′ = −
2
2
2
2 0
5
10 2
210 2
10 2 2
4 10
5 4,
2 5
y
x x
x x y
x xx
x x
x
x y
−− =−
− + = −
− + = −
− + = −=
= =
The point 5 4
,2 5
is on the graph of f. The slope of the
tangent line is 5 8
.2 25
f ′ = −
Tangent line:4 8 5
5 25 2
25 20 8 20
8 25 40 0
y x
y x
x y
− = − −
− = − ++ − =
83. (a) One possible secant is between ( )3.9, 7.7019 and ( )4, 8 :
( )
( )( )
8 7.70198 4
4 3.9
8 2.981 4
2.981 3.924
y x
y x
y S x x
−− = −−
− = −
= = −
(b) ( ) ( ) ( )
( ) ( )
1 23 34 2 3
2 2
3 4 8 3 4
f x x f
T x x x
′ ′= = =
= − + = −
The slope (and equation) of the secant line approaches that of the tangent line at
( )4, 8 as you choose points closer and closer to ( )4, 8 .
(c) As you move further away from ( )4, 8 , the accuracy of the approximation T gets worse.
(d)
–3 –2 –1 –0.5 –0.1 0 0.1 0.5 1 2 3
1 2.828 5.196 6.548 7.702 8 8.302 9.546 11.180 14.697 18.520
–1 2 5 6.5 7.7 8 8.3 9.5 11 14 17
−2
−2 12
(4, 8)
20
−2
−2 12T
f
20
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Section 2.2 Basic Differentiation Rules and Rates of Change 137
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84. (a) Nearby point: ( )1.0073138, 1.0221024
( )
( )
1.0221024 1Secant line: 1 1
1.0073138 1
3.022 1 1
y x
y x
−− = −−
= − +
(Answers will vary.)
(b) ( )( ) ( )
23
3 1 1 3 2
f x x
T x x x
′ =
= − + = −
(c) The accuracy worsens as you move away from ( )1, 1 .
(d)
The accuracy decreases more rapidly than in Exercise 85 because 3y x= is less “linear” than 3 2.y x=
85. False. Let ( )f x x= and ( ) 1.g x x= + Then
( ) ( ) ,f x g x x′ ′= = but ( ) ( ).f x g x≠
86. True. If 2 ,ay x bx+= + then
( ) ( ) ( )2 1 12 2 .a adya x b a x b
dx+ − += + + = + +
87. False. If 2,y π= then 0.dy dx = ( 2π is a constant.)
88. True. If ( ) ( ) ,f x g x b= − + then
( ) ( ) ( )0 .f x g x g x′ ′ ′= − + = −
89. False. If ( ) 0,f x = then ( ) 0f x′ = by the Constant Rule.
90. False. If ( ) 1,n
n
f x xx
−= = then
( ) 11.n
n
nf x nx
x− −
+−′ = − =
91. ( ) [ ]3 5, 1, 2= +f t t
( ) 3.′ =f t So, ( ) ( )1 2 3.′ ′= =f f
Instantaneous rate of change is the constant 3.
Average rate of change:
( ) ( )2 1 11 8
32 1 1
− −= =−
f f
92. ( ) [ ]( )
2 7, 3, 3.1
2
f t t
f t t
= −
′ =
Instantaneous rate of change:
At ( ) ( )3, 2 : 3 6f ′ =
At ( ) ( )3.1, 2.61 : 3.1 6.2f ′ =
Average rate of change:
( ) ( )3.1 3 2.61 2
6.13.1 3 0.1
f f− −= =−
93. ( ) [ ]
( ) 2
1, 1, 2
1
f xx
f xx
= −
′ =
Instantaneous rate of change:
( ) ( )
( )
1, 1 1 1
1 12, 2
2 4
f
f
′− =
′− =
Average rate of change:
( ) ( ) ( ) ( )2 1 1 2 1 1
2 1 2 1 2
f f− − − −= =
− −
–3 –2 –1 –0.5 –0.1 0 0.1 0.5 1 2 3
–8 –1 0 0.125 0.729 1 1.331 3.375 8 27 64
–8 –5 –2 –0.5 0.7 1 1.3 2.5 4 7 10
−3 3
−2
(1, 1)
2
−3 3
−2
fT
2
(1, 1)
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138 Chapter 2 Differentiation
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94. ( )
( )
sin , 0,6
cos
f x x
f x x
π = ′ =
Instantaneous rate of change:
( ) ( )0, 0 0 1
1 3, 0.866
6 2 6 2
f
fπ π
′ =
′ = ≈
Average rate of change:
( ) ( )( )
( )( )
6 0 1 2 0 30.955
6 0 6 0
f fππ π π
− −= = ≈
− −
95. (a) ( )( )
216 1362
32
s t t
v t t
= − +
= −
(b) ( ) ( )2 1
1298 1346 48 ft/sec2 1
s s−= − = −
−
(c) ( ) ( ) 32v t s t t′= = −
When ( )1: 1 32 ft/sect v= = −
When ( )2: 2 64 ft/sect v= = −
(d) 2
2
16 1362 0
1362 13629.226 sec
16 4
t
t t
− + =
= = ≈
(e) 1362 1362
324 4
8 1362 295.242 ft/sec
v
= −
= − ≈ −
96. ( )( )( )( )
( )
( )( )
( ) ( )
2
2
2
16 22 220
32 22
3 118 ft/sec
16 22 220
112 height after falling 108 ft
16 22 108 0
2 2 8 27 0
2
2 32 2 22
86 ft/sec
s t t t
v t t
v
s t t t
t t
t t
t
v
= − − +
= − −
= −
= − − +
=
− − + =
− − + =
=
= − −
= −
97. ( )
( )( ) ( )
( ) ( )
20 0
2
4.9
4.9 120
9.8 120
5 9.8 5 120 71 m/sec
10 9.8 10 120 22 m/sec
s t t v t s
t t
v t t
v
v
= − + +
= − +
= − +
= − + =
= − + =
98. (a) ( )( ) ( )
2 20 04.9 4.9 214
9.8
s t t v t s t
s t v t t
= − + + = − +
′ = = −
(b) ( ) ( )5 2
Average velocity5 2
91.5 194.4
334.3 m/sec
−=
−−=
= −
s s
(c) ( ) ( )( ) ( )2 9.8 2 19.6 m/sec
5 9.8 5 49.0 m/sec
s
s
′ = − = −
′ = − =
(d) ( ) 2
2
2
4.9 214 0
4.9 214
214
4.96.61 sec
= − + =
=
=
≈
s t t
t
t
t
(e) ( ) ( )6.61 9.8 6.61 64.8 m/secv = − ≈ −
99. From ( )0, 0 to ( ) ( ) ( )1 12 2
4, 2 , mi/min.s t t v t= =
( ) ( )12
60 30 mi/hv t = = for 0 4t< <
Similarly, ( ) 0v t = for 4 6.t< < Finally, from ( )6, 2
to ( )10, 6 ,
( ) ( )4 1 mi/min. 60 mi/h.s t t v t= − = =
(The velocity has been converted to miles per hour.)
100. This graph corresponds with Exercise 101.
101. 3 2, 3dV
V s sds
= =
When 36 cm, 108 cmdV
sds
= = per cm change in s.
t
Time (in minutes)2 4 6 8 10
10
20
30
40
50
60
Vel
ocity
(in
mi/h
)
v
t2 4 6 8 10
2
6
10
4
8
(0, 0)
(4, 2)(6, 2)
(10, 6)
Dis
tanc
e (i
n m
iles)
Time (in minutes)
s
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Section 2.2 Basic Differentiation Rules and Rates of Change 139
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102. 2 , 2dA
A s sds
= =
When 6 m,s = 212 mdA
ds= per m change in s.
103. (a) Using a graphing utility,
( ) 0.417 0.02.R v v= −
(b) Using a graphing utility,
( ) 20.0056 0.001 0.04.B v v v= + +
(c) ( ) ( ) ( ) 20.0056 0.418 0.02T v R v B v v v= + = + +
(d)
(e) 0.0112 0.418dT
vdv
= +
For ( )40, 40 0.866v T ′= ≈
For ( )80, 80 1.314v T ′= ≈
For ( )100, 100 1.538v T ′= ≈
(f ) For increasing speeds, the total stopping distance increases.
104. ( )( )
( )
2
gallons of fuel used cost per gallon
15,000 52,2003.48
52,200
C
x x
dC
dx x
=
= =
= −
The driver who gets 15 miles per gallon would benefit more. The rate of change at 15x = is larger in absolute value than that at 35.x =
105. ( ) 21
2s t at c= − + and ( )s t at′ = −
( ) ( )( ) ( )
( ) ( ) ( ) ( ) )
( ) ( )( ) ( ) ( )( )
( )
2 20 00 0
0 0
2 22 20 0 0 0
00 0 0
1 2 1 2Average velocity:
2
1 2 2 1 2 2
2
2instantaneous velocity at
2
a t t c a t t cs t t s t t
t t t t t
a t t t t a t t t t
t
at tat s t t t
t
− + Δ + − − − Δ ++ Δ − − Δ =+ Δ − − Δ Δ
− + Δ + Δ + − Δ + Δ=
Δ− Δ ′= = − = =
Δ
106.
( ) ( )
1,008,0006.3
1,008,0006.3
351 350 5083.095 5085 $1.91
C QQ
dC
dQ Q
C C
= +
= − +
− ≈ − ≈ −
When 350, $1.93.dC
QdQ
= ≈ −
1200
0
TB
R
80
x 10 15 20 25 30 35 40
C 5220 3480 2610 2088 1740 1491.4 1305
–522 –232 –130.5 –83.52 –58 –42.61 –32.63
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140 Chapter 2 Differentiation
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107. 2y ax bx c= + +
Because the parabola passes through ( )0, 1 and ( )1, 0 , you have:
( ) ( ) ( )( ) ( ) ( )
2
2
0, 1 : 1 0 0 1
1, 0 : 0 1 1 1 1
a b c c
a b b a
= + + =
= + + = − −
So, ( )2 1 1.y ax a x= + − − + From the tangent line 1,y x= − you know that the derivative is 1 at the point ( )1, 0 .
( )( ) ( )
2 1
1 2 1 1
1 1
2
1 3
y ax a
a a
a
a
b a
′ = + − −
= + − −
= −== − − = −
Therefore, 22 3 1.y x x= − +
108.
2
1, 0
1
y xx
yx
= >
′ = −
At ( ), ,a b the equation of the tangent line is ( )2 2
1 1 2or .
xy x a y
a a a a− = − − = − +
The x-intercept is ( )2 , 0 .a The y-intercept is 2
0, .a
The area of the triangle is ( )1 1 22 2.
2 2A bh a
a = = =
109. 3
2
9
3 9
y x x
y x
= −
′ = −
Tangent lines through ( )1, 9 :−
( )( )
( )( )
2
3 3 2
3 2 2
32
9 3 9 1
9 9 3 3 9 9
0 2 3 2 3
0 or
y x x
x x x x x
x x x x
x x
+ = − −
− + = − − +
= − = −
= =
The points of tangency are ( )0, 0 and ( )3 812 8, .− At ( )0, 0 , the slope is ( )0 9.y′ = − At ( )3 81
2 8, ,− the slope is ( )3 9
2 4.y′ = −
Tangent Lines:
( ) ( )81 9 38 4 2
9 274 4
0 9 0 and
9
9 0 9 4 27 0
− = − − + = − −
= − = − −+ = + + =
y x y x
y x y x
x y x y
x1 2 3
1
2
)a,(( , ) =a b 1a
y
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Section 2.2 Basic Differentiation Rules and Rates of Change 141
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110. 2
2
y x
y x
=′ =
(a) Tangent lines through ( )0, :a
( )2 2
2
2 0
2
y a x x
x a x
a x
a x
− = −
− =
− =
± − =
The points of tangency are ( ), .a a± − − At ( ), ,a a− − the slope is ( ) 2 .y a a′ − = −
At ( ), ,a a− − − the slope is ( ) 2 .y a a′ − − = − −
( ) ( )Tangent lines: 2 and 2
2 2
y a a x a y a a x a
y ax a y ax a
+ = − − − + = − − + −
= − + = − − +
Restriction: a must be negative.
(b) Tangent lines through ( ), 0 :a
( )
( )
2 2
2
0 2
2 2
0 2 2
y x x a
x x ax
x ax x x a
− = −
= −
= − = −
The points of tangency are ( )0, 0 and ( )22 , 4 .a a At ( )0, 0 , the slope is ( )0 0.y′ = At ( )22 , 4 ,a a the slope is ( )2 4 .y a a′ =
( ) ( )2
2
Tangent lines: 0 0 0 and 4 4 2
0 4 4
y x y a a x a
y y ax a
− = − − = −= = −
Restriction: None, a can be any real number.
111. ( )3
2
, 2
, 2
ax xf x
x b x
≤= + >
f must be continuous at 2x = to be differentiable at 2.x =
( )
( ) ( )
3
2 2
2
2 2
lim lim 88 4
8 4lim lim 4
x x
x x
f x ax aa b
a bf x x b b
− −→ →
+ +→ →
= == +
− == + = +
( )23 , 2
2 , 2
ax xf x
x x
<′ = >
For f to be differentiable at 2,x = the left derivative must equal the right derivative.
( ) ( )2
13
43
3 2 2 2
12 4
8 4
a
a
a
b a
=
=
=
= − = −
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142 Chapter 2 Differentiation
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112. ( )cos , 0
, 0
x xf x
ax b x
<= + ≥
( ) ( )0 cos 0 1 1f b b= = = =
( )sin , 0
, 0
x xf x
a x
− <′ = >
So, 0.a =
Answer: 0, 1a b= =
113. ( )1 sinf x x= is differentiable for all ,x n nπ≠ an
integer.
( )2 sinf x x= is differentiable for all 0.x ≠
You can verify this by graphing 1f and 2f and observing
the locations of the sharp turns.
114. Let ( ) cos .f x x=
( ) ( ) ( )
( )
( )
0
0
0 0
lim
cos cos sin sin coslim
cos cos 1 sinlim lim sin
0 sin 1 sin
x
x
x x
f x x f xf x
xx x x x x
x
x x xx
x x
x x
Δ →
Δ →
Δ → Δ →
+ Δ −′ =
ΔΔ − Δ −=
ΔΔ − Δ = − Δ Δ
= − = −
115. You are given :f R R→ satisfying
( ) ( ) ( ) ( )*
f x n f xf x
n
+ −′ = for all real numbers x and
all positive integers n. You claim that
( ) , , .f x mx b m b R= + ∈
For this case,
( ) ( ) [ ].
m x n b mx bf x m m
n
+ + − + ′ = = =
Furthermore, these are the only solutions:
Note first that ( ) ( ) ( )2 11 ,
1
f x f xf x
+ − +′ + = and
( ) ( ) ( )1 .f x f x f x′ = + − From ( )* you have
( ) ( ) ( )( ) ( ) ( ) ( )( ) ( )
2 2
2 1 1
1 .
f x f x f x
f x f x f x f x
f x f x
′ = + −
= + − + + + − ′ ′= + +
Thus, ( ) ( )1 .f x f x′ ′= +
Let ( ) ( ) ( )1 .g x f x f x= + −
Let ( ) ( ) ( )0 1 0 .m g f f= = −
Let ( )0 .b f= Then
( ) ( ) ( )( ) ( )( ) ( ) ( ) ( )
( )
1 0
constant 0
1
.
g x f x f x
g x g m
f x f x f x g x m
f x mx b
′ ′ ′= + − =
= = =
′ = + − = =
= +
Section 2.3 Product and Quotient Rules and Higher-Order Derivatives
1. To find the derivative of the product of two differentiable functions f and g, multiply the first function f by the derivative of the second function g, and then add the second function g times the derivative of the first function f.
2. To find the derivative of the quotient of two differentiable functions f and ,g where ( ) 0,g x ≠ multiply the
denominator by the derivative of the numerator minus the numerator times the derivative of the denominator, all of which is divided by the square of the denominator.
3. 2
2
tan sec
cot csc
sec sec tan
csc csc cot
dx x
dxd
x xdxd
x x xdxd
x x xdx
=
= −
=
= −
4. Higher-order derivatives are successive derivatives of a function.
5. ( ) ( )( )( ) ( )( ) ( )( )
2 3 1 5
2 3 5 1 5 2
10 15 2 10
20 17
= − −
′ = − − + −
= − + + −= − +
g x x x
g x x x
x x
x
6. ( )( )( )( ) ( )( )
3
2 3
3 2 3
3 2
3 4 5
3 4 3 5 3
9 12 3 15
12 12 15
y x x
y x x x
x x x
x x
= − +
′ = − + +
= − + +
= − +
7. ( ) ( ) ( )( ) ( ) ( )
2 1 2 2
1 2 2 1 2
3 2 3 21 2
3 21 2
2 2
1 2
1 1
12 1
21 1
22 2
5 1
2 2
1 5 1 5
2 2
−
= − = −
′ = − + −
= − + −
= − +
− −= =
h t t t t t
h t t t t t
t tt
tt
t t
t t
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Section 2.3 Product and Quotient Rules and Higher-Order Derivatives 143
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8. ( ) ( ) ( )( ) ( ) ( )
2 1 2 2
1 2 2 1 2
3 2 3 2 1 2
3 21 2
2
8 8
12 8
21
2 42
5 4
2
5 8
2
g s s s s s
g s s s s s
s s s
ss
s
s
−
−
= + = +
′ = + +
= + +
= +
+=
9. ( )( ) ( ) ( )
( )
3
3 2
2 3
2
cos
sin cos 3
3 cos sin
3 cos sin
f x x x
f x x x x x
x x x x
x x x x
=
′ = − +
= −
= −
10. ( )
( )
sin
1cos sin
2
1cos sin
2
g x x x
g x x x xx
x x xx
=
′ = +
= +
11. ( )
( ) ( )( ) ( )( ) ( ) ( )2 2 2
5
5 1 1 5 5
5 5 5
xf x
x
x x x xf x
x x x
=−− − − −′ = = = −
− − −
12. ( )
( )( )( ) ( )( )
( )
( )
( )
2
2
2
2 2
2
2
2
3 1
2 5
2 5 6 3 1 2
2 5
12 30 6 2
2 5
6 30 2
2 5
tg t
t
t t tg t
t
t t t
t
t t
t
−=++ − −
′ =+
+ − +=+
+ +=+
13. ( )
( )( ) ( )
( )
( )
( )
1 2
3 3
3 1 2 1 2 2
23
3 3
21 2 3
3
23
1 11
1 32
1
1 6
2 1
1 5
2 1
−
= =+ +
+ −′ =
+
+ −=+
−=+
x xh x
x x
x x x xh x
x
x x
x x
x
x x
14. ( )2
2 1
xf x
x=
+
( ) ( )( ) ( )( )
( )
( )( )
( )
2 1 2
2
3 2 3 2
2
3 2
2
2
2 1 2
2 1
4 2
2 1
3 2
2 1
3 2
2 1
−+ −′ =
+
+ −=+
+=+
+=
+
x x x xf x
x
x x x
x
x x
x
x x
x
15. ( )
( ) ( ) ( )( )
2
2
2 32
sin
cos sin 2 cos 2 sin
xg x
x
x x x x x x xg x
xx
=
− −′ = =
16. ( )
( )( ) ( )
( )
3
3 2
2 43
cos
sin cos 3 sin 3 cos
tf t
t
t t t t t t tf t
tt
=
− − +′ = = −
17. ( ) ( )( )( ) ( )( ) ( )( )
( )
3 2
3 2 2
4 2 3 4 3 2 2
4 3 2
4 3 2 5
4 6 2 3 2 5 3 4
6 24 2 8 9 6 15 12 8 20
15 8 21 16 20
0 20
= + + −
′ = + + + + − +
= + + + + + − + + −
= + + + −′ = −
f x x x x x
f x x x x x x x
x x x x x x x x x
x x x x
f
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144 Chapter 2 Differentiation
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18. ( ) ( )( )
( )( ) ( )( )
( ) ( ) ( )
2
2
2 2
2
2
2 3 9 4
2 3 9 9 4 4 3
18 27 36 16 27 12
54 38 12
1 54 1 38 1 12 80
f x x x x
x x x x
x x x x x
x x
f
= − +
= − + + −
= − + + − −
= − −
′ − = − − − − =
19.
( )
( )( )( ) ( )( )
( )
( )
( )
( )( )
2
2
2
2 2
2
2
2
2
4
3
3 2 4 1
3
2 6 4
3
6 4
3
1 6 4 11
41 3
xf x
x
x x xf x
x
x x x
x
x x
x
f
−=−− − −
′ =−
− − +=−
− +=−
− +′ = = −−
20.
( )
( ) ( )( ) ( )( )( )
( )
( )
( )( )
2
2
2
2
4
4
4 1 4 1
4
4 4
4
8
4
8 83
493 4
xf x
x
x xf x
x
x x
x
x
f
−=++ − −
′ =+
+ − +=+
=+
′ = =+
21. ( )( ) ( )( ) ( )( )
( )
cos
sin cos 1 cos sin
2 2 24
4 2 4 2 8
f x x x
f x x x x x x x
fπ π π
=
′ = − + = −
′ = − = −
22.
( )
( ) ( )( ) ( )( )
( )( ) ( )
( )
2
2
2
2
2
sin
cos sin 1
cos sin
6 3 2 1 2
6 36
3 3 18
3 3 6
xf x
x
x x xf x
xx x x
x
fππ
π
πππ
π
=
−′ =
−=
− ′ =
−=
−=
Function Rewrite Differentiate Simplify
23. 3 6
3
+= x xy 31
23
= +y x x ( )213 2
3′ = +y x 2 2′ = +y x
24. 25 3
4
xy
−= 25 3
4 4y x= −
10
4y x′ =
5
2
xy′ =
25. 2
6
7y
x= 26
7y x−= 312
7y x−′ = −
3
12
7y
x′ = −
26. 3
10
3y
x= 310
3y x−= 430
3y x−′ = −
4
10y
x′ = −
27. 3 24x
yx
= 1 24 , 0y x x= > 1 22y x−′ = 2
, 0y xx
′ = >
28. 1 3
2xy
x= 2 32y x= 1 34
3y x−′ =
1 3
4
3y
x′ =
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Section 2.3 Product and Quotient Rules and Higher-Order Derivatives 145
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29.
( )
( ) ( )( ) ( )( )( )
( )
( )( )
( )( )
( ) ( ) ( )
2
2
2 2
22
2 3 2 3
22
2
22
2
22
2
2 2 2
4 3
1
1 3 2 4 3 2
1
3 3 2 2 8 6 2
1
3 6 3
1
3 2 1
1
3 1 3, 1
1 1 1
x xf x
x
x x x x xf x
x
x x x x x x
x
x x
x
x x
x
xx
x x x
− −=−
− − − − − −′ =
−
− + − + − + +=−
− +=−
− +=
−
−= = ≠
− + +
30. ( )
( ) ( )( ) ( )( )( )
( )
( )( )
( ) ( )( )
( ) ( )
( )
2
2
2 2
22
3 2 3 2
22
2
22
2
2 2
2
2 2
2
5 6
4
4 2 5 5 6 2
4
2 5 8 20 2 10 12
4
5 20 20
4
5 4 4
2 2
5 2
2 2
5, 2, 2
2
x xf x
x
x x x x xf x
x
x x x x x x
x
x x
x
x x
x x
x
x x
xx
+ +=−
− + − + +′ =
−
+ − − − − −=−
− − −=−
− + +=
− +
− +=
− +
= − ≠ −−
Alternate solution:
( )
( )( )( )( )
2
2
5 6
4
3 2
2 2
3, 2
2
x xf x
x
x x
x x
xx
x
+ +=−
+ +=
+ −
+= ≠ −−
( ) ( )( ) ( )( )( )
( )
2
2
2 1 3 1
2
5
2
x xf x
x
x
− − +′ =
−
= −−
31. ( )
( ) ( ) ( )( )
( )( )
( )
2
2
2
2
2
4 41
3 3
3 4 4 11
3
6 9 12
3
6 3
3
= − = − + + + −
′ = −+
+ + −=
+
+ −=+
xf x x x
x x
x xf x
x
x x
x
x x
x
32. ( )
( ) ( ) ( )( )
( )
( ) ( )( )
( )
4 4
4 32
24 3
2 2
23
2
2 11
1 1
1 1 14
11
2 14
1 1
2 22
1
− = − = + + + − − − ′ = + + + − = + + + + − = +
xf x x x
x x
x x xf x x x
xx
xx x
x x
x xx
x
33. ( )
( )
1 2 1 2
1 2 3 23 2
3 13
3 1 3 1
2 2 2
−
− −
−= = −
+′ = + =
xf x x x
xx
f x x xx
Alternate solution:
( )
( )( ) ( ) ( )
( )
1 2
1 2 1 2
1 2
3 2
3 1 3 1
13 3 1
2
13 1
2
3 1
2
−
−
− −= =
− − ′ =
+=
+=
x xf x
xx
x x xf x
x
x x
xx
x
34. ( ) ( ) ( )( ) ( )
3 1 3 1 2
1 3 1 2 1 2 2 3
1 6 2 3
1 6 2 3
3 3
1 13
2 3
5
65 1
6
− −
− −
= + = +
′ = + +
= +
= +
f x x x x x
f x x x x x
x x
x x
Alternate solution:
( ) ( )( )
3 5 6 1 3
1 6 2 31 6 2 3
3 3
5 5 1
6 6− −
= + = +
′ = + = +
f x x x x x
f x x xx x
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146 Chapter 2 Differentiation
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35. ( ) ( )( )
( ) ( ) ( )( )( )
( )
( ) ( )
2
2
22
2 2
22
2 2
2 222
2 1 2 1 2 1
3 3 3
3 2 2 1 2 3
3
2 6 4 8 3
3
2 2 3 2 2 3
33
x x xf x
x x x x x
x x x xf x
x x
x x x x
x x
x x x x
x xx x
− − −= = =− − −
− − − −′ =
−
− − + −=−
− + − − += =−−
36. ( )
( ) ( )( ) ( )( )( )
( )
( )
( )
3
3 2
3 2 2 3 2
23 2
5 4 2 5 4
24
4 2
24
3
23
12
5 1 5
1
15 1 5 3 2
15 15 3 2 15 10
1
5 3 2
1
5 3 2
1
xx x
h xx x x
x x x x x xh x
x x
x x x x x x
x x
x x x
x x
x x
x x
+ += =+ ++ − + +
′ =+
+ − − − −=+
− −=+
− −=+
37. ( )
( ) ( ) ( )( )
( )( ) ( )
( )( )
( )
( )( )
( )
43 3
3 42
2
4 32
2
22 4 3
2
2 2 4 3
2
4 3 2
2
2 2
2
5 52 2
2 4 115
2
3 815
2
15 2 3 8
2
15 4 4 3 8
2
12 52 60
2
4 3 13 15
2
s sg s s s
s s
s s sg s s
s
s ss
s
s s s s
s
s s s s s
s
s s s
s
s s s
s
= − = − + +
+ −′ = −+
+= −+
+ − +=
+
+ + − −=
+
+ +=+
+ +=
+
38. ( )
( ) ( ) ( )( )
( )( ) ( )
22
2 22 2
2 2 2
2 12
1 1
2 2 1 21 2 1 2 22
1 1 1
xg x x x
x x x
x x x xx x x x xg x
x x x
= − = − + +
+ + − −+ − + +′ = − = =+ + +
39. ( ) ( )( )( )( ) ( )( )( ) ( )( )( ) ( )( )( )
( )( ) ( )( ) ( )( )( ) ( ) ( )
3
2 3 3
2 2 3 3
4 2 3 2 4 3 2 4 2 3
4 3 2
2 5 3 2
6 5 3 2 2 5 1 2 2 5 3 1
6 5 6 2 5 2 2 5 3
6 5 6 5 36 30 2 4 5 10 2 5 6 15
10 8 21 10 30
f x x x x x
f x x x x x x x x x x
x x x x x x x x x
x x x x x x x x x x x x x
x x x x
= + − +
′ = + − + + + + + + −
= + − − + + + + + −
= + − − − − + + + + + + − −
= − − − −
Note: You could simplify first: ( ) ( )( )3 22 5 6f x x x x x= + − −
40. ( ) ( )( )( )( ) ( )( )( ) ( )( )( ) ( )( )( )
( )( ) ( )( ) ( )( )
( )( )( )
3 2 2
2 2 2 3 2 3 2
4 2 2 4 2 2 5 3
6 4 2 5 3 4 2
6 4 5 3 4 2
6 4 2 5 3
6 5 3
2 1
3 1 2 1 2 1 2 2 1
3 5 2 1 2 2 1 2 2 1
3 5 2 3 5 2 3 5 2
2 2 2 2 2 2
2 2 4 2
7 6 4 9
f x x x x x x
f x x x x x x x x x x x x x x
x x x x x x x x x x x x
x x x x x x x x
x x x x x x
x x x x x x
x x x x2
= − + + −
′ = − + + − + − + − + − + +
= + − + − + − + − + + − +
= + − + + − − − +
+ − + − − +
+ + − + + −
= + + − − 4 2x +
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Section 2.3 Product and Quotient Rules and Higher-Order Derivatives 147
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41. ( )( ) ( )
2
2
sin
cos 2 sin cos 2 sin
f t t t
f t t t t t t t t t
=
′ = + = +
42. ( ) ( )( ) ( )( ) ( )( )
( )
1 cos
1 sin cos 1
cos 1 sin
f
f
θ θ θ
θ θ θ θ
θ θ θ
= +
′ = + − +
= − +
43. ( )
( ) 2 2
cos
sin cos sin cos
tf t
tt t t t t t
f tt t
=
− − +′ = = −
44. ( )
( ) ( )( )
3
3 2
2 43
sin
cos sin 3 cos 3 sin
xf x
x
x x x x x x xf x
xx
=
− −′ = =
45. ( )( ) 2 2
tan
1 sec tan
f x x x
f x x x
= − +
′ = − + =
46. 2 2
cot
1 csc cot
y x x
y x x
= +
′ = − = −
47. ( )
( )
4 1 4
3 4
3 4
6 csc 6 csc
16 csc cot
41
6 csc cot4
g t t t t t
g t t t t
t tt
−
= + = +
′ = −
= −
48. ( )
( )
1
2
2
112 sec 12 sec
12 sec tan
112 sec tan
h x x x xx
h x x x x
x xx
−
−
= − = −
′ = − −
−= −
49. ( )
( )( ) ( )( )( )
( )
( )
2
2 2
2
2
3 1 sin 3 3 sin
2 cos 2 cos
3 cos 2 cos 3 3 sin 2 sin
2 cos
6 cos 6 sin 6 sin
4 cos 3
1 tan sec tan 23
sec tan sec 2
x xy
x x
x x x xy
x
x x x
x
x x x
x x x
− −= =
− − − −′ =
− + −=
= − + −
= −
50.
( )2
2
sec
sec tan sec
sec tan 1
xy
xx x x x
yx
x x x
x
=
−′ =
−=
51.
( )2
2
2
csc sin
csc cot cos
coscos
sin
cos csc 1
cos cot
= − −′ = −
= −
= −
=
y x x
y x x x
xx
x
x x
x x
52. sin cos
cos sin sin cos
y x x x
y x x x x x x
= +′ = + − =
53. ( )( ) ( )
2
2 2 2
tan
sec 2 tan sec 2 tan
f x x x
f x x x x x x x x x
=
′ = + = +
54. ( )( ) ( ) ( )
sin cos
sin sin cos cos cos 2
f x x x
f x x x x x x
=
′ = − + =
55.
( )( )
2
2
2
2 sin cos
2 cos 2 sin sin 2 cos
4 cos 2 sin
y x x x x
y x x x x x x x
x x x x
= +
′ = + + − +
= + −
56. ( )( ) 2
5 sec tan
5 sec tan 5 sec sec tan
h
h
θ θ θ θ θ
θ θ θ θ θ θ θ θ
= +
′ = + + +
57. ( ) ( )
( ) ( ) ( ) ( )( ) ( )( )( )
( )
2
2
2
12 5
2
2 1 1 112 2 5
2 2
2 8 1
2
+ = − + + − ++ ′ = + − + +
+ −=+
xg x x
x
x xxg x x
x x
x x
x
( )Form of answer may vary.
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148 Chapter 2 Differentiation
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58. ( )
( ) ( )( ) ( )( )( )
( )
( )
2
2 2
2
2
cos
1 sin
1 sin sin cos cos
1 sin
sin sin cos
1 sin
1 sin
1 sin
1
1 sin
xf x
x
x x x xf x
x
x x x
x
x
x
x
=−
− − − −′ =
−
− + +=−
−=−
=−
(Form of answer may vary.)
59.
( )( ) ( )( )( ) ( )
( )( )( )
2 2
2
1 csc
1 csc
1 csc csc cot 1 csc csc cot 2 csc cot
1 csc 1 csc
2 2 34 3
6 1 2
xy
x
x x x x x x x xy
x x
yπ
+=−
− − − + −′ = =− −
− ′ = = − −
60. ( )( )( )
tan cot 1
0
1 0
f x x x
f x
f
= =
′ =
′ =
61. ( )
( ) ( ) ( )( ) ( )
( ) ( )2 2
2 2
sec
sec tan sec 1 sec tan 1
sec tan 1 1
th t
t
t t t t t t th t
t t
hπ π π
ππ π
=
− −′ = =
−′ = =
62. ( ) ( )( ) ( ) ( )
2 2
sin sin cos
sin cos sin sin cos cos
sin cos sin sin cos cos
sin 2 cos 2
sin cos 14 2 2
f x x x x
f x x x x x x x
x x x x x x
x x
fπ π π
= +
′ = − + +
= − + += +
′ = + =
63. (a) ( ) ( )( ) ( )( ) ( )( ) ( )( )
( ) ( )
3
3
3 3 2
3 2
4 1 2 , 1, 4
4 1 1 2 3 4
4 1 3 6 4 8
4 6 8 9
1 3; Slope at 1, 4
f x x x x
f x x x x x
x x x x x
x x x
f
2
= + − − −
′ = + − + − +
= + − + − + −
= − + −′ = − −
Tangent line: ( )4 3 1 3 1y x y x+ = − − = − −
(b)
(c) Graphing utility confirms 3dy
dx= − at ( )1, 4 .−
64. (a) ( ) ( )( ) ( )( ) ( )( ) ( )( )
( ) ( )
2
2
2 2
2
2 4 , 1, 5
2 2 4 1
2 4 4
3 4 4
1 3; Slope at 1, 5
f x x x
f x x x x
x x x
x x
f
= − + −
′ = − + +
= − + +
= − +′ = − −
Tangent line:
( ) ( )5 3 1 3 8y x y x− − = − = −
(b)
(c) Graphing utility confirms 3dy
dx= at ( )1, 5 .−
−6
−1 3
3
(1, −4)
−15
−3 6
(1, −5)
3
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65. (a) ( ) ( )
( ) ( )( ) ( )( ) ( )
( )( )
( )
2 2
2
, 5, 54
4 1 1 4
4 4
45 4; Slope at 5, 5
5 4
xf x
x
x xf x
x x
f
= −++ −
′ = =+ +
′ − = = −− +
Tangent line: ( )5 4 5 4 25y x y x− = + = +
(b)
(c) Graphing utility confirms 4dy
dx= at ( )5, 5 .−
66. (a) ( ) ( )
( ) ( )( ) ( )( )( ) ( )
( ) ( )
2 2
3, 4, 7
3
3 1 3 1 6
3 3
64 6; Slope at 4, 7
1
xf x
x
x xf x
x x
f
+=−− − +′ = = −
− −
−′ = = −
Tangent line:
( )7 6 4 6 31y x y x− = − − = − +
(b)
(c) Graphing utility confirms 6dy
dx= − at ( )4, 7 .
67. (a) ( )
( ) 2
tan , , 14
sec
2; Slope at , 14 4
f x x
f x x
f
π
π π
=
′ =
′ =
Tangent line: 1 24
1 22
4 2 2 0
y x
y x
x y
π
π
π
− = −
− = −
− − + =
(b)
(c) Graphing utility confirms 2dy
dx= at , 1 .
4
π
68. (a) ( )
( )
sec , , 23
sec tan
2 3; Slope at , 23 3
f x x
f x x x
f
π
π π
=
′ =
′ =
Tangent line:
2 2 33
6 3 3 6 2 3 0
y x
x y
π
π
− = −
− + − =
(b)
(c) Graphing utility confirms 2 3dy
dx= at , 2 .
3
π
69. ( ) ( )
( ) ( )( ) ( )( ) ( )
( ) ( )( )
2
2
2 22 2
2
8; 2, 1
4
4 0 8 2 16
4 4
16 2 12
24 4
f xx
x x xf x
x x
f
=++ − −′ = =
+ +
−′ = = −
+
( )11 2
21
22
2 4 0
y x
y x
y x
− = − −
= − +
+ − =
70. ( )
( ) ( )( ) ( )( ) ( )
( ) ( )( )
2
2
2 22 2
2
27 3; 3,
9 2
9 0 27 2 54
9 9
54 3 13
29 9
f xx
x x xf x
x x
f
= − +
+ − −′ = =+ +
− −′ − = =
+
( )3 13
2 21
32
2 6 0
y x
y x
y x
− = +
= +
− − =
−6
−8 1
8
(−5, 5)
−8
−5 10
(4, 7)
8
−4
4
−
π4( (, 1
ππ
−
−2
6
π π
π3( (, 2
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150 Chapter 2 Differentiation
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71. ( )
( ) ( )( ) ( )( ) ( )
( ) ( )
2
2 2
2 22 2
2
16 8; 2,
16 5
16 16 16 2 256 16
16 16
256 16 4 122
20 25
xf x
x
x x x xf x
x x
f
= − − +
+ − −′ = =+ +
−′ − = =
( )8 122
5 2512 16
25 2525 12 16 0
y x
y x
y x
+ = +
= −
− + =
72. ( )
( ) ( )( ) ( )( ) ( )
( )
2
2 2
2 22 2
2
4 4; 2,
6 5
6 4 4 2 24 4
6 6
24 16 22
10 25
xf x
x
x x x xf x
x x
f
= +
+ − −′ = =+ +
−′ = =
( )4 22
5 252 16
25 2525 2 16 0
y x
y x
y x
− = −
= +
− − =
73. ( )
( ) ( )
1 22
2 33
2 12
2 12 2
xf x x x
x
xf x x x
x
− −
− −
−= = −
− +′ = − + =
( ) 0f x′ = when 1,x = and ( )1 1.f =
Horizontal tangent at ( )1, 1 .
74. ( )
( ) ( )( ) ( )( )( )
( )
2
2
2 2
22
22
1
1 2 2
1
2
1
xf x
x
x x x xf x
x
x
x
=++ −
′ =+
=+
( ) 0f x′ = when 0.x =
Horizontal tangent is at ( )0, 0 .
75. ( )
( ) ( )( ) ( )( )
( )( )
( )
2
2
2
2
2 2
1
1 2 1
1
22
1 1
xf x
x
x x xf x
x
x xx x
x x
=−− −
′ =−
−−= =− −
( ) 0f x′ = when 0x = or 2.x =
Horizontal tangents are at ( )0, 0 and ( )2, 4 .
76. ( )
( ) ( )( ) ( )( )( )
( )
( )( )( )
( )
2
2
22
2 2
22
2
2 22 2
4
7
7 1 4 2
7
7 2 8
7
7 18 7
7 7
−=−− − −
′ =−
− − +=−
− −− += − = −− −
xf x
x
x x xf x
x
x x x
x
x xx x
x x
( ) 0f x′ = for ( ) ( )1 11, 7; 1 , 7
2 14x f f= = =
f has horizontal tangents at 1
1,2
and 1
7, .14
77. ( )
( ) ( ) ( )( ) ( )2 2
1
11 1 2
1 1
+=−− − + −′ = =
− −
xf x
xx x
f xx x
1
2 6 3;2
y x y x+ = = − + Slope: 1
2−
( )( )
( ) ( )
2
2
2 1
21
1 4
1 2
1, 3; 1 0, 3 2
− = −−
− =− = ±
= − − = =
x
x
x
x f f
( )
( )
1 1 10 1
2 2 21 1 7
2 32 2 2
y x y x
y x y x
− = − + = − −
− = − − = − +
−2 2 4 6
−4
−6
6
(3, 2)(−1, 0)
2y + x = −1
2y + x = 7y
x
f (x) = x + 1x − 1
−2−4−6
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Section 2.3 Product and Quotient Rules and Higher-Order Derivatives 151
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78. ( )
( ) ( )( ) ( )2 2
1
1 1
1 1
xf x
x
x xf x
x x
=−
− − −′ = =− −
Let ( ) ( )( ), , 1x y x x x= − be a point of tangency on the
graph of f.
( )( )( )
( )( ) ( )( )( )
( )( )
2
2
2
5 1 1
1 1
4 5 1
1 1 1
4 5 1 1
4 10 4 0
12 2 1 0 , 2
2
x x
x x
x
x x x
x x x
x x
x x x
− − −=− − −
− =− + −
− − = +
− + =
− − = =
( ) ( )1 11, 2 2; 4, 2 1
2 2f f f f ′ ′= − = = − = −
Two tangent lines:
( )
11 4 4 1
2
2 1 2 4
y x y x
y x y x
+ = − − = − +
− = − − = − +
79. ( ) ( ) ( )( ) ( )
( ) ( ) ( )( )( ) ( )
( ) ( ) ( ) ( ) ( )
2 2
2 2
2 3 3 1 6
2 2
2 5 5 4 1 6
2 2
5 4 3 2 42
2 2 2
x xf x
x x
x xg x
x x
x x xg x f x
x x x
+ −′ = =+ +
+ − +′ = =+ +
+ += = + = ++ + +
f and g differ by a constant.
80. ( ) ( ) ( )( )
( ) ( ) ( )( )
( ) ( )
2 2
2 2
cos 3 sin 3 1 cos sin
cos 2 sin 2 1 cos sin
sin 2 sin 3 55
x x x x x x xf x
x x
x x x x x x xg x
x xx x x x x
g x f xx x
− − − −′ = =
+ − + −′ = =
+ − += = = +
f and g differ by a constant.
81. (a) ( ) ( ) ( ) ( ) ( )
( ) ( ) ( ) ( ) ( ) ( ) 11 1 1 1 1 1 4 6 1
2
p x f x g x f x g x
p f g f g
′ ′ ′= +
′ ′ ′= + = + − =
(b) ( ) ( ) ( ) ( ) ( )( )
( ) ( ) ( )
2
2
3 1 7 0 14
3 3
g x f x f x g xq x
g x
q
′ ′−′ =
− −′ = = −
82. (a) ( ) ( ) ( ) ( ) ( )
( ) ( ) ( )14 8 1 0 4
2
p x f x g x f x g x
p
′ ′ ′= +
′ = + =
(b) ( ) ( ) ( ) ( ) ( )( )
( ) ( ) ( )
2
2
4 2 4 1 12 37
4 16 4
g x f x f x g xq x
g x
q
′ ′−′ =
− −′ = = =
83. ( ) ( )
( )
3 2 1 2
1 2 1 2 2
Area 6 5 6 5
5 18 59 cm /sec
2 2
A t t t t t
tA t t t
t−
= = + = +
+′ = + =
84. ( ) ( )2 3 2 1 21 12 2
2 2V r h t t t tπ π π = = + = +
( ) 1 2 1 2 31 2
1 3 3 2in. /sec
2 2 4
tV t t t
tπ π− + ′ = + =
85.
( )
2
23
200100 , 1
30
400 30100
30
xC x
x x
dC
dx x x
= + ≤ +
= − + +
x
y
(2, 2)
(−1, 5)
, −1 12( )
−2−4 2 4
−2
6
y = −4x + 1
y = −x + 4
f(x) = xx − 1
(a) When
(b) When
(c) When
As the order size increases, the cost per item decreases.
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152 Chapter 2 Differentiation
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86. ( )
( ) ( )( ) ( )( )( ) ( ) ( )
( )
2
2 2 2
2 2 22 2 2
4500 1
50
50 4 4 2 200 4 50500 500 2000
50 50 50
2 31.55 bacteria/h
tP t
t
t t t t tP t
t t t
P
= + +
+ − − − ′ = = = + + +
′ ≈
87. (a)
[ ] ( )( ) ( )( )( )2
1sec
cos
cos 0 1 sin1 sin 1 sinsec sec tan
cos cos cos cos coscos
xx
x xd d x xx x x
dx dx x x x x xx
=
− − = = = = ⋅ =
(b)
[ ] ( )( ) ( )( )( )2
1csc
sin
sin 0 1 cos1 cos 1 coscsc csc cot
sin sin sin sin sinsin
xx
x xd d x xx x x
dx dx x x x x xx
=
− = = = − = − ⋅ = −
(c)
[ ] ( ) ( )( )( )
22
2 2 2
coscot
sin
sin sin cos coscos sin cos 1cot csc
sin sin sinsin
xx
x
x x x xd d x x xx x
dx dx x x xx
2
=
− − += = = − = − = −
88. ( )( ) [ )( ) ( )
sec
csc , 0, 2
f x x
g x x
f x g x
π
=
=
′ ′=
3
33
1 sinsec tan sincos cos
sec tan csc cot 1 1 1 tan 1 tan 11 coscsc cot cos
sin sin
xx x xx x
x x x x x xxx x x
x x
⋅= − = − = − = − = − = −
⋅
3 7
,4 4
xπ π=
89. (a) ( )( )
101.7 1593
2.1 287
= +
= +
h t t
p t t
(b)
(c) 101.7 1593
2.1 287
+=+
tA
t
A represents the average health care expenditures per person (in thousands of dollars).
(d) ( ) 2
25,842.6
4.41 1205.4 82,369′ ≈
+ +A t
t t
( )A t′ represents the rate of change of the average
health care expenditures per person for the given year t.
90. (a)
( )
sin
csc
csc csc 1
r
r hr h r
h r r r
θ
θθ θ
=+
+ =
= − = −
(b) ( ) ( )
( )
( )
csc cot
306
4000 2 3 8000 3 mi / rad
θ θ θ
π
′ = − ⋅
′ ′° =
= − ⋅ = −
h r
h h
23007 14
3000
3007 14
320
07 14
10
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Section 2.3 Product and Quotient Rules and Higher-Order Derivatives 153
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91. ( )( )( )
2 7 4
2 7
2
f x x x
f x x
f x
= + −
′ = +
′′ =
92. ( )( )( )
5 3 2
4 2
3
4 2 5
20 6 10
80 12 10
f x x x x
f x x x x
f x x x
= − +
′ = − +
′′ = − +
93. ( )( )
( )
3 2
1 2
1 2
4
6
33
f x x
f x x
f x xx
−
=
′ =
′′ = =
94. ( )( )
( )
2 3
4
55
3
2 9
362 36 2
f x x x
f x x x
f x xx
−
−
−
= +
′ = −
′′ = + = +
95. ( )
( ) ( )( ) ( )( ) ( )
( )( )
2 2
3
1
1 1 1 1
1 1
2
1
xf x
x
x xf x
x x
f xx
=−− − −′ = =
− −
′′ =−
96.
( )
( )( )( ) ( )( )
( )
( )
( ) ( ) ( ) ( )( )( )
( ) ( )( ) ( )( )
( )( ) ( )( )
( )
( )
2
2
2
2 2 2
2 2
2 2
4
2
4
2
3
2 2
3
3
3
4
4 2 3 3 1
4
2 5 12 3 8 12
8 164
4 2 8 8 12 2 8
4
4 4 2 8 2 8 12
4
4 2 8 2 8 12
4
2 16 32 2 16 24
4
56
4
x xf x
x
x x x xf x
x
x x x x x x
x xx
x x x x xf x
x
x x x x x
x
x x x x
x
x x x x
x
x
+=−− + − +
′ =−
− − − − − −= =− +−
− − − − − −′′ =
−
− − − − − − =−
− − − − −=
−
− + − + +=−
=−
97. ( )( )( ) ( )
sin
cos sin
sin cos cos
sin 2 cos
f x x x
f x x x x
f x x x x x
x x x
=
′ = +
′′ = − + +
= − +
98. ( )( )( ) ( )
cos
cos sin
sin sin cos cos 2 sin
=
′ = −
′′ = − − + = − −
f x x x
f x x x x
f x x x x x x x x
99. ( )( )( ) ( ) ( )2
3 2
csc
csc cot
csc csc cot csc cot
csc cot csc
f x x
f x x x
f x x x x x x
x x x
=
′ = − +
′′ = − − − −
= +
100. ( )( )( ) ( ) ( )
( )
2
2 2
sec
sec tan
sec sec tan sec tan
sec sec tan
f x x
f x x x
f x x x x x x
x x x
=
′ =
′′ = +
= +
101. ( )
( )
( )
3 2 5
2 3 5
8 58 5
23
56 6
6 625 25
f x x x
f x x x
f x x x xx
−
−
′ = −
′′ = −
′′′ = + = +
102. ( ) ( )( ) ( )
53 4 4 5
4 1 51 5
4 4
5 5
f x x x
f x xx
−
= =
= =
103. ( )( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )
3
4
5
6
7
8
sin
cos
sin
cos
sin
cos
sin
f x x
f x x
f x x
f x x
f x x
f x x
f x x
′′ = −
= −
=
=
= −
= −
=
104. ( ) ( )( ) ( )
4
5
cos
cos sin
f t t t
f t t t t
=
= −
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154 Chapter 2 Differentiation
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105. ( ) ( ) ( )( ) ( ) ( )( ) ( ) ( )
( )
2
2
2 2 2 2
2 2 4
0
f x g x h x
f x g x h x
f g h
= +
′ ′ ′= +
′ ′ ′= +
= − +
=
106. ( ) ( )( ) ( )( ) ( )
4
2 2 4
f x h x
f x h x
f h
= −
′ ′= −
′ ′= − = −
107. ( ) ( )( )
( ) ( ) ( ) ( ) ( )( )
( ) ( ) ( ) ( ) ( )( )
( )( ) ( )( )( )
2
2
2
2 2 2 22
2
1 2 3 4
1
10
g xf x
h x
h x g x g x h xf x
h x
h g g hf
h
=
′ ′−′ =
′ ′−
′ =
− − −=
−
= −
108. ( ) ( ) ( )( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( ) ( )
( )( ) ( )( )2 2 2 2 2
3 4 1 2
14
f x g x h x
f x g x h x h x g x
f g h h g
=
′ ′ ′= +
′ ′ ′= +
= + − −
=
109. Polynomials of degree 1n − (or lower) satisfy( ) ( ) 0.nf x = The derivative of a polynomial of the 0th
degree (a constant) is 0.
110. To differentiate a piecewise function, separate the function into its pieces, and differentiate each piece.
If ( ) ,f x x x= then on ( ), 0−∞ you have ( ) 2 ,f x x= − ( ) 2 ,f x x′ = − and ( ) 2.f x′′ = −
On ( )0, ∞ you have ( ) 2,f x x= ( ) 2 ,f x x′ = and ( ) 2.f x′′ =
Notice that ( ) ( )0 0, 0 0,f f ′= = but ( )0f ′′ does not exist (the left-hand limit is 2,− whereas the right-hand limit is 2).
111. It appears that f is cubic, so
f ′ would be quadratic and
f ′′ would be linear.
112. It appears that f is quadratic
so f ′ would be linear and
f ′′ would be constant.
113.
114.
115. The graph of a differentiable function f such that
( )2 0, 0f f ′= < for 2,x−∞ < < and 0f ′ > for
2 x< < ∞ would, in general, look like the graph below.
One such function is ( ) ( )22 .f x x= −
2
2
1
1−1−2x
f
y
f ′
f ″
x2 3 4
−1
−2
−1
3
−2
ff ′
f ″
y
−1−2−3 1 2 3 4 5
−3
−4
−5
1
2
3
4
x
y
f ′
f ″
−1
−2
−3
−4
1
y
x
f ′ f ″
2π π2
x
1
1
2
2
3
3 4
4
y
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Section 2.3 Product and Quotient Rules and Higher-Order Derivatives 155
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116. The graph of a differentiable function f such that 0f >and 0f ′ < for all real numbers x would, in general,
look like the graph below.
117. ( )( ) ( )( )( )
2
2
36 , 0 6
2
3 27 m/sec
3 6 m/sec
v t t t
a t v t t
v
a
= − ≤ ≤′= = −
=
= −
The speed of the object is decreasing.
118. ( )
( ) ( ) ( )( ) ( )( )( ) ( )2 2
100
2 15
2 15 100 100 2 1500
2 15 2 15
tv t
t
t ta t v t
t t
=+
+ −′= = =+ +
(a) ( )( )
22
15005 2.4 ft/sec
2 5 15a = =
+
(b) ( )( )
22
150010 1.2 ft/sec
2 10 15a = ≈
+
(c) ( )( )
22
150020 0.5 ft/sec
2 20 15a = ≈
+
119. ( )( ) ( )( ) ( )
28.25 66
16.50 66
16.50
s t t t
v t s t t
a t v t
= − +′= = +′= = −
Average velocity on:
[ ]
[ ]
[ ]
[ ]
57.75 00, 1 is 57.75
1 099 57.75
1, 2 is 41.252 1
123.75 992, 3 is 24.75
3 2132 123.75
3, 4 is 8.254 3
− =−
− =−
− =−
− =−
120. (a) s position function
v velocity function
a acceleration function
(b) The speed of the particle is the absolute value of its velocity. So, the particle’s speed is slowing
down on the intervals ( )0, 4 3 and ( )8 3, 4 and it speeds up on the intervals ( )4 3, 8 3 and ( )4, 6 .
x
f
y
t(sec) 0 1 2 3 4
s(t) (ft) 0 57.75 99 123.75 132
66 49.5 33 16.5 0
–16.5 –16.5 –16.5 –16.5 –16.5
y
t1−1 4 5 6 7
8
4
12
16
s
v
a
1 3 5 6 7−4
−8
−12
−16
4
8
12
16
t
t =t = 44
3
t = 83 v
speed
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156 Chapter 2 Differentiation
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121. ( )( ) ( ) ( )( ) ( )( )1 2 2 1 !
n
n
f x x
f x n n n n
=
= − − =
Note: ( ) ( )! 1 3 2 1 read “ factorial”n n n n= − ⋅ ⋅
122. ( )
( ) ( ) ( ) ( )( )( ) ( )( ) ( )1 1
1
1 1 2 2 1 1 !n n
nn n
f xx
n n n nf x
x x+ +
=
− − − −= =
123. ( ) ( ) ( )f x g x h x=
(a) ( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )
( ) ( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )
( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )4 4
2
2 2
3 3
3 3 3
f x g x h x h x g x
f x g x h x g x h x h x g x h x g x
g x h x g x h x h x g x
f x g x h x g x h x g x h x g x h x h x g x h x g x
g x h x g x h x g x h x g x h x
f x g x h x g x h x g x h x g x h x
′ ′ ′= +
′′ ′′ ′ ′ ′′ ′ ′= + + +
′′ ′ ′ ′′= + +
′′′ ′′′ ′ ′′ ′ ′′ ′′ ′ ′′′ ′ ′′= + + + + +
′′′ ′ ′′ ′′ ′ ′′′= + + +
′ ′′′ ′ ′′′ ′′ ′′ ′′= + + + + ( ) ( ) ( ) ( )( ) ( ) ( ) ( ) ( )
( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )
4
4 4
3
4 6 4
g x h x g x h x
g x h x g x h x
g x h x g x h x g x h x g x h x g x h x
′′ ′′′ ′+
′′′ ′+ +
′ ′′′ ′′ ′′ ′′′ ′= + + + +
(b)
( ) ( ) ( ) ( ) ( ) ( )( ) ( )( )( )( ) ( )( ) ( ) ( ) ( ) ( )( ) ( )( )
( )( ) ( )( ) ( )( ) ( ) ( ) ( )
( )( ) ( )( )( )( )( ) ( )( ) ( )( ) ( ) ( ) ( )
( )( ) ( )( )( )( ) ( )( ) ( )
( ) ( ) ( ) ( ) ( ) ( )
( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )
1 2
3
1
1 2
1 2 2 1 1 2 2 1
1 1 2 2 1 2 1 2 3 2 1
1 2 2 1
3 2 1 3 4 2 1
1 2 2 1
1 2 2 1 1
! !
1! 1 ! 2! 2 !
n n n n
n
n n
n n n
n n n n n nf x g x h x g x h x g x h x
n n n n
n n ng x h x
n n
n n ng x h x g x h x
n n
n ng x h x g x h x g x h x
n n
n
− −
−
−
− −
− − − −′ ′′= + +
− − − − − −
′′′+ + − −
− −′+ +
− −
′ ′′= + + +− −
+
( )( ) ( ) ( ) ( ) ( ) ( )1!
1 !1!n ng x h x g x h x
n− ′ +
−
Note: ( )! 1 3 2 1n n n= − ⋅ ⋅ (read “n factorial”)
124. ( ) ( ) ( )
( ) ( ) ( ) ( ) ( ) ( )
( ) ( ) ( ) ( ) ( ) ( )
2
2 3
xf x xf x f x
xf x xf x f x f x xf x f x
xf x xf x f x f x xf x f x
′ ′ = +
′′ ′′ ′ ′ ′′ ′ = + + = +
′′′ ′′′ ′′ ′′ ′′′ ′′ = + + = +
In general, ( ) ( ) ( ) ( ) ( ) ( )1 .n n nxf x xf x nf x− = +
125. ( )( ) 1
sin
cos sin
n
n n
f x x x
f x x x nx x−
=
′ = +
When ( )1: cos sinn f x x x x′= = +
When ( ) 22: cos 2 sinn f x x x x′= = +
When ( ) 3 23: cos 3 sinn f x x x x x′= = +
When ( ) 4 34: cos 4 sinn f x x x x x′= = +
For general ( ) 1, cos sin .n nn f x x x nx x−′ = +
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126. ( )
( )( )
1
1
1
coscos
sin cos
sin cos
sin cos
nn
n n
n
n
xf x x x
x
f x x x nx x
x x x n x
x x n x
x
−
− − −
− −
+
= =
′ = − −
= − +
+= −
When ( ) 2
sin cos1:
x x xn f x
x
+′= = −
When ( ) 3
sin 2 cos2:
x x xn f x
x
+′= = −
When ( ) 4
sin 3 cos3:
x x xn f x
x
+′= = −
When ( ) 5
sin 4 cos4:
x x xn f x
x
+′= = −
For general ( ) 1
sin cos, .
n
x x n xn f x
x ++′ = −
127. 2 3
3 2 3 23 2
1 1 2, ,
2 12 2 2 2 0
y y yx x x
x y x y x xx x
′ ′′= = − =
′′ ′+ = + − = − =
128.
( ) ( )
3
2
2 2
2 6 10
6 6
12
12
2 –12 12 2 6 6 24
y x x
y x
y x
y
y xy y x x x x
= − +
′ = −′′ =′′′ =
′′′ ′′ ′− − − = − − − = −
129.
( )
2 sin 3
2 cos
2 sin
2 sin 2 sin 3 3
y x
y x
y x
y y x x
= +′ =′′ = −
′′ + = − + + =
130.
( ) ( )
3 cos sin
3 sin cos
3 cos sin
3 cos sin 3 cos sin 0
y x x
y x x
y x x
y y x x x x
= +′ = − +′′ = − −
′′ + = − − + + =
131. False. If ( ) ( ),y f x g x= then
( ) ( ) ( ) ( ).dyf x g x g x f x
dx′ ′= +
132. True. y is a fourth-degree polynomial.
0n
n
d y
dx= when 4.n >
133. True
( ) ( ) ( ) ( ) ( )( )( ) ( )( )0 0
0
h c f c g c g c f c
f c g c
′ ′ ′= +
= +
=
134. True
135. True
136. True
137. ( ) ( ) ( ) ( ) ( )( ) ( )
( ) ( ) ( ) ( ) ( ) ( )
( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )
d df x g x h x f x g x h x
dx dxd
f x g x h x f x g x h xdx
f x g x g x f x h x f x g x h x
f x g x h x f x g x h x f x g x h x
=
′= +
′ ′ ′= + + ′ ′ ′= + +
138. (a) ( )True
fg f g fg f g f g f g
fg f g
′′ ′ ′′ ′ ′ ′ ′ ′′− = + − −
′′ ′′= −
(b) ( ) ( )
2
False
fg fg f g
fg f g f g f g
fg f g f g
fg f g
′′ ′′ ′= +
′′ ′ ′ ′ ′ ′′= + + +′′ ′ ′ ′′= + +′′ ′′≠ +
Section 2.4 The Chain Rule
1. To find the derivative of the composition of two differentiable functions, take the derivative of the outer function and keep the inner function the same. Then multiply this by the derivative of the inner function.
( )( ) ( )( ) ( )f g x f g x g x′ ′ ′=
2. The (Simple) Power Rule is ( ) 1.n ndx nx
dx−= The
General Power Rule uses the Chain Rule:
( ) 1 .n nd duu nu
dx dx−=
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158 Chapter 2 Differentiation
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( )( )=y f g x ( )=u g x ( )=y f u
3. ( )46 5y x= − 6 5u x= − 4y u=
4. 3 4 3y x= + 4 3u x= + 1 3y u=
5. 1
3 5y
x=
+ 3 5u x= +
1y
u=
6. 2
2
10y
x=
+ 2 10u x= +
2y
u=
7. 3cscy x= cscu x= 3y u=
8. 5
sin2
xy =
5
2
xu = siny u=
9. ( )( ) ( )( )
3
2
2
2 7
3 2 7 2
6 2 7
y x
y x
x
= −
′ = −
= −
10. ( )( )( ) ( ) ( )
( )
43
3 33 2 2 3
32 3
5 2
5 4 2 3 60 2
60 2
y x
y x x x x
x x
= −
′ = − − = − −
= −
11. ( ) ( )
( ) ( ) ( )
( )
( )
5 6
1 6
1 6
1 6
3 4 9
53 4 9 9
6
454 9
245
2 4 9
−
−
= −
′ = − −
−= −
= −−
g x x
g x x
x
x
12. ( ) ( )
( ) ( ) ( )
2 3
1 3
3
9 2
2 69 2 9
3 9 2
f t t
f t tt
−
= +
′ = + =+
13. ( ) ( )( ) ( ) ( )
( )
1 22 2
1 22
1 2 22
2 5 3 2 5 3
12 5 3 10
2
10 10
5 35 3
−
= − + = − +
′ = − + −= = −
++
h s s s
h s s s
s s
ss
14. ( ) ( )( ) ( ) ( )
1 22 2
1 22
2
4 3 4 3
1 34 3 6
2 4 3
g x x x
xg x x x
x
−
= − = −
′ = − − = −−
15. ( )( ) ( )
( ) ( )
1 33 2 2
2 322 3 22 23
6 1 6 1
1 4 46 1 12
3 6 1 6 1
y x x
x xy x x
x x
−
= + = +
′ = + = =+ +
16. ( )( ) ( )
( ) ( )
1 44 2 2
3 42
3 4 32 24
2 9 2 9
12 9 2
4
9 9
y x x
y x x
x x
x x
−
= − = −
′ = − −
− −= =− −
17. ( )
( ) ( )( )
1
2
2
2
11 2 1
2
y x
y xx
−
−
= −
−′ = − − =−
18. ( ) ( )( ) ( ) ( )
( ) ( )
122
22
2 22 2
14 5
4 5
4 5 5 2
5 2 2 5
4 5 5 4
s t t tt t
s t t t t
t t
t t t t
−
−
= = − −− −
′ = − − − − −
+ += =− − + −
19. ( )( )
( )
( ) ( )( ) ( )
( )
3333
43 2
2
43
66 2
2
6 3 2 3
54
2
g s ss
g s s s
s
s
−
−
= = −−
′ = − −
= −−
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Section 2.4 The Chain Rule 159
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20. ( )
( )
( )( )
4
4
5
5
33 2
2
1212 2
2
y tt
y tt
−
−
= − = − −−
′ = − =−
21. ( )
( ) ( )
( )
( )
1 2
3 2
3 2
3
13 5
3 5
13 5 3
23
2 3 5
3
2 3 5
y xx
y x
x
x
−
−
= = ++
′ = − +
−=+
= −+
22. ( ) ( )
( ) ( ) ( )
( )
( )
1 22
2
3 22
3 22
32
12
2
12 2
2
2
2
g t tt
g t t t
t
t
t
t
−
−
= = −−
′ = − −
−=−
= −−
23. ( ) ( )( ) ( ) ( )
( ) ( )( ) ( )
72
7 6 2
6
6
2
2 2 7 2
2 2 2 7
2 9 4
f x x x
f x x x x x
x x x x
x x x
= −
′ = − + −
= − − +
= − −
24. ( ) ( )( ) ( )( ) ( ) ( ) ( )
( ) ( )( ) ( )
3
2 3
2
2
2 5
3 2 5 2 2 5 1
2 5 6 2 5
2 5 8 5
f x x x
f x x x x
x x x
x x
= −
′ = − + −
= − + −
= − −
25. ( )( ) ( ) ( ) ( )
( ) ( )( ) ( )
1 22 2
1 2 1 22 2
1 2 1 22 2 2
1 22 2 2
2
2
1 1
11 2 1 1
2
1 1
1 1
1 2
1
y x x x x
y x x x x
x x x
x x x
x
x
−
−
−
= − = −
′ = − − + −
= − − + −
= − − + −
−=−
26. ( )( ) ( ) ( )
( )( )
( )
1 22 2 2 2
1 2 1 22 2 2
2 21 22
2
2
16 16
12 16 16 2
2
2 1616
32 3
16
y x x x x
y x x x x x
xx x
x
x x
x
−
= − = −
′ = − + − −
= − − −
−=
−
27. ( )
( ) ( ) ( ) ( )
( )
( ) ( )
( )
( ) ( )
1 22 2
1 2 1 22 2
21 22
1 2 1 22 2 2
2
1 22 2 2
2
3 2 32 2
1 1
11 1 1 2
2
1
1 1
1
1 1
11 1
1 1
x xy
x x
x x x xy
x
x x x
x
x x x
x
x x
−
−
−
= =+ +
+ − + ′ =
+
+ − +=
+
+ + − =+
= =+ +
28.
( ) ( ) ( ) ( )
( ) ( ) ( )
4
1 2 1 24 4 3
4
4 4 4 4
3 2 3 2 34 4 4
4
14 1 4 4
24
4 2 4 4
4 4 4
xy
x
x x x xy
x
x x x x
x x x
−
=+
+ − +′ =
++ − − −= = =
+ + +
29. ( )
( ) ( ) ( )( )( )
( )( )( )
( )( )( )
2
2
2
22 2
2
32
2
32
5
2
2 5 252
2 2
2 5 2 10
2
2 5 10 2
2
xg x
x
x x xxg x
x x
x x x
x
x x x
x
+ = +
+ − ++ ′ = + +
+ − −=
+
− + + −=
+
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160 Chapter 2 Differentiation
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30. ( )
( ) ( )( ) ( )( )
( )( )
( )( )
22
3
3 2 22
23 3
2 4 3 3
3 33 3
2
2 2 32
2 2
2 4 2 4
2 2
th t
t
t t t tth t
t t
t t t t t
t t
= +
+ − ′ = + +
− −= =
+ +
31. ( )
( ) ( )( ) ( )( )( )
( ) ( )( )
( )( )
4
3
2
3
5
3
5
1
3
3 1 1 114
3 3
4 1 2
3
8 1
3
ts t
t
t tts t
t t
t
t
t
t
+ = +
+ − ++ ′ = + +
+=
+
+=
+
32. ( )
( ) ( )( ) ( )( )( )
( )( )( )
( )( )( )
2 22
2
2
22 2
2
32
2
32
3 2 2 3
2 3 3 2
3 2 2 2 3 62 32
3 2 3 2
2 2 3 6 18 4
3 2
4 2 3 3 9 2
3 2
x xg x
x x
x x xxg x
x x
x x x
x
x x x
x
− − + = = + −
− − ++ ′ = − −
+ − − −=
−
+ + += −
−
33. ( ) ( )( )( ) ( )( ) ( ) ( )( )
( ) ( ) ( ) ( ) ( ) ( )
252
5 42 2
9 5 4 9 5 42 2 2 2 2 2 2 2
3
2 3 5 3 2 1
2 10 3 3 10 3 20 3 2 3 20 3 2
f x x x
f x x x x x
x x x x x x x x x x x x
= + +
′ = + + + +
= + + + + + + = + + + + + +
34. ( ) ( )( )( ) ( )( ) ( ) ( )( ) ( ) ( )( )
342
2 24 3 3 42 2 2 2
2 1
3 2 1 4 1 2 24 1 2 1
g x x
g x x x x x x x
= + +
′ = + + + = + + +
35. cos 4
4 sin 4
y x
dyx
dx
=
= −
36. sin
cos
y x
dyx
dx
π
π π
=
=
37. ( )( ) 2
5 tan 3
15 sec 3
g x x
g x x
=
′ =
38. ( )( ) ( )
sec 6
sec 6 tan 6 6
6 sec 6 tan 6
h x x
h x x x
x x
=
′ =
=
39. ( ) ( )( ) ( )
( )
2 2 2
2 2 2 2 2 2
22
sin sin
cos 2 2 cos
2 cos
y x x
y x x x x
x x
π π
π π π π
π π
= =
′ = =
=
40. ( )( ) ( ) ( )( )
( ) ( ) ( )
2
2 2
2 2
csc 1 2
csc 1 2 cot 1 2 2 1 2 2
4 1 2 csc 1 2 cot 1 2
y x
y x x x
x x x
= −
′ = − − − − −
= − − −
41. ( )( ) ( ) ( )
2 2
sin 2 cos 2
sin 2 2 sin 2 cos 2 2 cos 2
2 cos 2 2 sin 2
2 cos 4
h x x x
h x x x x x
x x
x
=
′ = − +
= −=
Alternate solution: ( )( ) ( )
12
12
sin 4
cos 4 4 2 cos 4
h x x
h x x x
=
′ = =
42. ( )( ) ( ) ( ) ( ) ( ) ( )
( ) ( ) ( )
2
2 2
1 12 2
1 1 1 1 1 1 12 2 2 2 2 2 2
1 1 1 12 2 2 2
sec tan
sec sec tan sec tan
sec sec tan
g
g
θ θ θ
θ θ θ θ θ θ
θ θ θ
=
′ = +
= +
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Section 2.4 The Chain Rule 161
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43. ( )
( ) ( ) ( )
2
2
4
2 2 2
3 3
cot cos
sin sin
sin sin cos 2 sin cos
sin
sin 2 cos 1 cos
sin sin
x xf x
x x
x x x x xf x
x
x x x
x x
= =
− −′ =
− − − −= =
44. ( )
( ) ( ) ( )2 2
coscos sin
csc
cos cos sin sin
cos sin cos 2
vg v v v
v
g v v v v v
v v v
= = ⋅
′ = + −
= − =
45. 2
2
4 sec
8 sec sec tan 8 sec tan
y x
y x x x x x
=
′ = ⋅ =
46. ( ) ( )( ) ( )( )
( )( )
225 cos 5 cos
10 cos sin
10 sin cos
5 sin 2
g t t t
g t t t
t t
t
π π
π π π
π π ππ π
= =
′ = −
= −
= −
47. ( ) ( )( ) ( )( )( )( )
221 14 4
14
12
sin 2 sin 2
2 sin 2 cos 2 2
sin 2 cos 2 sin 4
f
f
θ θ θ
θ θ θ
θ θ θ
= =
′ =
= =
48. ( ) ( )( ) ( ) ( )( )
( ) ( )
2
2
2
2 cot 2
4 cot 2 csc 2
4 cot 2 csc 2
π
π π π
π π π
= +
′ = + − +
= − + +
h t t
h t t t
t t
49. ( ) ( )( ) ( ) ( ) ( )( )( )
( ) ( ) ( )
2
2 2
2 2
3 sec 1
3 sec 1 tan 1 2 1
6 1 sec 1 tan 1
f t t
f t t t t
t t t
π
π π π π
π π π π
= −
′′ = − − −
= − − −
50. ( )( ) ( )( )( )
( )
2
2
22
5 cos
5 sin 2
10 sin
y x
y x x
x x
π
π π π
π π
=
′ = −
= −
51. ( )( )( )
2
2
sin 3 cos
cos 3 cos 6 sin
y x x
y x x x x
= +
′ = + −
52. ( )( )( )
cos 5 csc
sin 5 csc 5 csc cot
y x x
y x x x x
= +
′ = − + −
53. ( )
( ) ( ) ( )( )
( ) ( )
1 2
1 2 1 2 2
2
sin cot 3 sin cot 3
1cos cot 3 cot 3 csc 3 3
2
3 cos cot 3 csc 3
2 cot 3
π π
π π π π
π π π
π
−
= =
′ = −
= −
y x x
y x x x
x x
x
54. ( )
( ) ( )( ) ( ) ( ) ( ) ( )( )
21/2 2
cos sin tan
sin sin tan cos tan sec1sin sin tan sin tan cos tan sec
2 2 sin tan
y x
x x xy x x x x
x
π
π π π ππ π π π π
π−
=
−′ = − ⋅ =
55.
( )
2
2 3 2
22
1
1
1 3 4
2 1
xy
x
x xy
x x
+=+
− −′ =+
The zero of y′ corresponds to the point on the graph of y
where the tangent line is horizontal.
56.
( )3 2
2
11
2 1
=+
′ =+
xy
x
yx x
y′ has no zeros.
57.
( )( )
1
1
2 1
+=
+′ = −
+
xy
x
x xy
x x
y′ has no zeros.
−2
−1 5
y
y ′
2
−6 6
−1
y
y ′
7
−2
−5 4
y
y ′
4
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58. ( )
( )
1 1
1 1
2 1 2 1
= − + +
′ = +− +
g x x x
g xx x
g′ has no zeros.
59.
2
2
cos 1
sin cos 1
sin cos 1
π
π π π
π π π
+=
− − −=
+ += −
xy
xdy x x x
dx xx x x
x
The zeros of y′ correspond to the points on the graph of
y where the tangent lines are horizontal.
60. 2
2
1tan
1 12 tan sec
y xx
dyx
dx x x
=
= −
The zeros of y′ correspond to the points on the graph of
y where the tangent lines are horizontal.
61.
( )
sin 3
3 cos 3
0 3
y x
y x
y
=′ =
′ =
3 cycles in [ ]0, 2π
62.
( )
sin2
1cos
2 21
02
=
′ =
′ =
xy
xy
y
[ ]1cycle in 0, 2
2π
63. ( ) ( )
( ) ( ) ( )( )
( )( )
1 22 2
1/221 2 22
2
8 8 , 1, 3
2 41 48 2 8
2 82 8
1 4 5 51
391 8 1
y x x x x
x xy x x x
x xx x
y
−
= + = +
+ +′ = + + = =++
+′ = = =+
64. ( ) ( )
( ) ( )
( )( )
1/53
4/53 2
2
4/53
3 4 , 2, 2
13 4 9 4
5
9 4
5 3 4
12
2
y x x
y x x x
x
x x
y
−
= +
′ = + +
+=+
′ =
65. ( ) ( )
( ) ( ) ( )( )
( )
13
223 223
15 2 , 2,
2
155 2 3
2
60 32
100 5
−
−
= − − −
−′ = − − =−
′ − = − = −
f x x
xf x x x
x
f
66. ( )( )
( )
( ) ( ) ( ) ( )( )
( )
2222
3232
1 13 , 4,
163
2 2 32 3 2 3
3
54
32
f x x xx x
xf x x x x
x x
f
−
−
= = − −
− −′ = − − − =
−
′ = −
67. ( )
( ) ( )
( )( )
( )
2
2
3
3
44 2 , 0, 1
2
88 2
2
80 1
8
y xx
y xx
y
−
−
= = ++
−′ = − + =+
−′ = = −
−2 10
−2
g
g′
6
−3
−5 5
y
y ′
3
−4 5
−6
y
y ′
6
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Section 2.4 The Chain Rule 163
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68. ( )
( ) ( )
( ) ( )
( ) ( ) ( )
3232
42
4
44 2 , 1, 4
2
12 2 2 2
1 12 1 0 0
y x xx x
y x x x
y
−
−
−
= = − −−
′ = − − −
′ = − − =
69. ( )
( )
3
2
3
26 sec 4 , 0, 25
3 sec 4 sec 4 tan 4 4
12 sec 4 tan 4
0 0
y x
y x x x
x x
y
= −
′ = −
= −′ =
70. ( )
( ) ( )
1 21
1 222
1 2cos cos , ,
2
1 1 sincos sin
2 2 cos
y x x xx
xy x x x
x x
ππ
−
−−
= + = +
′ = − + − = − −
( )/2y π′ is undefined.
71. (a) ( ) ( ) ( )
( ) ( ) ( )
( )
1/22
1/22
2
2 7 , 4, 5
1 22 7 4
2 2 7
84
5
f x x
xf x x x
x
f
−
= −
′ = − =−
′ =
Tangent line:
( )85 4 8 5 7 0
5y x x y− = − − − =
(b)
72. (a) ( ) ( ) ( )
( ) ( ) ( ) ( )
( ) ( ) ( )
1 22 2
1/2 1/22 2
22
2
1 15 5 , 2, 2
3 3
1 1 15 2 5
3 2 3
15
32 5
4 1 132 3
3 3 3 9
f x x x x x
f x x x x x
xx
x
f
−
= + = +
′ = + + +
= + ++
′ = + =
Tangent line:
( )132 2 13 9 8 0
9y x x y− = − − − =
(b)
73. (a) ( ) ( )( )( ) ( )
( )
23
3 2 2 3
4 3 , 1, 1
2 4 3 12 24 4 3
1 24
y x
y x x x x
y
= + −
′ = + = +
′ − = −
Tangent line:
( )1 24 1 24 23 0y x x y− = − + + + =
(b)
74. (a) ( ) ( ) ( )
( ) ( ) ( )( )
( )( )
2/32
1/321/32
1/3
9 , 1, 4
2 49 2
3 3 9
4 21
33 8
f x x
xf x x x
x
f
−
= −
−′ = − − =−
−′ = = −
Tangent line:
( )24 1 2 3 14 0
3y x x y− = − − + − =
(b)
75. (a) ( ) ( )( )( )
sin 8 , , 0
8 cos 8
8
f x x
f x x
f
π
π
=
′ =
′ =
Tangent line: ( )8 8 8y x xπ π= − = −
(b)
−2
−6 6
6
(4, 5)
−9 9
−6
6
−2
−2 1
14
(−1, 1)
6
5
−1
−2
(1, 4)
0
2
−2
2
( , 0)π
π
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164 Chapter 2 Differentiation
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76. (a) 2
cos 3 , ,4 2
3 sin 3
3 3 23 sin
4 4 2
y x
y x
y
π
π π
= −
′ = −
− ′ = − =
Tangent line:2 3 2
2 2 4
3 2 3 2 2
2 8 2
y x
y x
π
π
− + = −
−= + −
(b)
77. (a) ( )
( )
( )( )
2
2
tan , , 14
2 tan sec
2 1 2 44
f x x
f x x x
f
π
π
=
′ =
′ = =
Tangent line:
( )1 4 4 1 04
y x x yπ π − = − − + − =
(b)
78. (a)
( )( )
3
2 2
2 tan , ,24
6 tan sec
6 1 2 124
y x
y x x
y
π
π
=
′ = ⋅
′ = =
Tangent line:
( )2 12 12 2 3 04
y x x yπ π − = − − + − =
(b)
79. ( ) ( ) ( )
( ) ( )( )
( )
1 22 2
2
2
25 25 , 3, 4
125 2
2 25
33
4
f x x x
xf x x x
x
f
= − = −
−′ = − − =−
′ = −
Tangent line:
( )34 3 3 4 25 0
4y x x y− = − − + − =
80. ( ) ( ) ( )
( )( )
( )
1 22
2
3 22
2 , 1, 12
2for 0
2
1 2
xf x x x
x
f x xx
f
−= = −
−
′ = >−
′ =
Tangent line: ( )1 2 1 2 1 0y x x y− = − − − =
2
−2
2π
2π−
π4 2
2( (, −
−
−4
π π
4
π4( (, 1
3
−1
2π
2π−
π4( (, 2
9
−4
−9
8
(3, 4)
3
2
−1
−2(1, 1)
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Section 2.4 The Chain Rule 165
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81. ( )( )
( )( )
2
2
2 cos sin 2 , 0 2
2 sin 2 cos 2
2 sin 2 4 sin 0
2 sin sin 1 0
sin 1 2 sin 1 0
3sin 1
21 5
sin ,2 6 6
3 5Horizontal tangents at , ,
6 2 6
π
π
π π
π π π
= + < <′ = − +
= − + − =+ − =
+ − =
= − =
= =
=
f x x x x
f x x x
x x
x x
x x
x x
x x
x
Horizontal tangent at the points3 3 3
, , , 0 ,6 2 2
π π
and 5 3 3
,6 2
π −
82. ( )
( )( ) ( ) ( )( )( ) ( )
( )( )( )
( )
( )
1 2 1 2
3 2
3 2
12
4
2 1
2 1 4 4 2 1 2
2 1
2 1 4 4
2 1
4 4
2 1
−
−=−
− − + −′ =
−
− − +=
−−=−
xf x
x
x x xf x
x
x x
x
x
x
( )( )2 2
4 40 1
2 1
xf x x
x
−′ = = =−
Horizontal tangent at ( )1, 4−
83. ( ) ( )( ) ( ) ( ) ( )( ) ( ) ( ) ( )
4
3 3
2 2
5 2 7
20 2 7 7 140 2 7
420 2 7 7 2940 2 7
f x x
f x x x
f x x x
= −
′ = − − = − −
′′ = − − − = −
84. ( ) ( )( ) ( ) ( ) ( )( ) ( )( )( ) ( )
( )( )( )
33
2 23 2 2 3
22 3 2 3
3 3 3
3 3
6 4
18 4 3 54 4
54 2 4 3 108 4
108 4 3 4
432 4 1
f x x
f x x x x x
f x x x x x x
x x x x
x x x
= +
′ = + = +
′′ = + + +
= + + +
= + +
85. ( ) ( )
( ) ( ) ( )( ) ( ) ( )
( )
( )
1
2
3
3
3
111 6
11 6
11 6 11
22 11 6 11
242 11 6
242
11 6
−
−
−
−
= = −−
′ = − −
′′ = − −
= −
=−
f x xx
f x x
f x x
x
x
86. ( )( )
( )
( ) ( )
( ) ( )( )
2
2
3
4
4
88 2
2
16 2
4848 2
2
f x xx
f x x
f x xx
−
−
−
= = −−
′ = − −
′′ = − =−
87. ( )( )( ) ( )
( )
2
2
2 2
2 2 2
sin
2 cos
2 2 sin 2 cos
2 cos 2 sin
f x x
f x x x
f x x x x x
x x x
=
′ =
′′ = − +
= −
88. ( )( ) ( )
( ) ( )( ) ( )
( )( )
2
2
2 2 2
2 4 2 2 2
2 2 2 2
2 2 2
sec
2 sec sec tan
2 sec tan
2 sec sec 2 tan 2 sec tan
2 sec 4 sec tan
2 sec sec 2 tan
2 sec 3 sec 2
ππ π π π
π π π
π π π π π π π π π
π π π π π
π π π π
π π π
=′ =
=
′′ = +
= +
= +
= −
f x x
f x x x x
x x
f x x x x x x
x x x
x x x
x x
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166 Chapter 2 Differentiation
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89. ( ) ( ) ( )( ) ( ) ( ) ( )( ) ( )( )( )
3
2 2
6419 9
19
3 1 , 1,
3 3 1 3 3 1
2 3 1 3 18 6
1 24
h x x
h x x x
h x x x
h
= +
′ = + = +
′′ = + = +
′′ =
90. ( ) ( )
( ) ( )
( ) ( )( )
( )
1 2
3 2
5 2
5 2
1 14 , 0,
24
14
23 3
44 4 4
30
128
−
−
−
= = + +
′ = − +
′′ = + =+
′′ =
f x xx
f x x
f x xx
f
91. ( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )
( ) ( )( )
2
2 2
2 2
2 2 2
cos , 0, 1
sin 2 2 sin
2 cos 2 2 sin
4 cos 2 sin
0 0
=
′ = − = −
′′ = − −
= − −
′′ =
f x x
f x x x x x
f x x x x x
x x x
f
92. ( )
( ) ( )( ) ( ) ( ) ( )
( ) ( )
2
2
tan 2 , , 36
2 sec 2
4 sec 2 sec 2 tan 2 2
8 sec 2 tan 2
32 36
π
π
=
′ =′′ = ⋅
=
′′ =
g t t
g t t
g t t t t
t t
g
93.
The zeros of f ′ correspond to the points where the graph
of f has horizontal tangents.
94.
f is decreasing on ( ), 1−∞ − so f ′ must be negative there.
f is increasing on ( )1, ∞ so f ′ must be positive there.
95. (a) ( ) ( )( ) ( )( ) ( ) ( )
3
3 3 3 3
g x f x
g x f x g x f x
=
′ ′ ′ ′= =
The rate of change of g is three times as fast as the
rate of change of .f
(b) ( ) ( )( ) ( )( ) ( ) ( )
2
2 22 2
g x f x
g x f x x g x x f x
=
′ ′ ′ ′= =
The rate of change of g is 2x times as fast as the rate
of change of .f
96. ( )( )2
2 5
3 1
xr x
x
−=+
(a) If ( ) ( )( )
,f x
h xg x
= then write ( ) ( ) ( )( ) 1h x f x g x
−=
and use the Product Rule.
(b) ( ) ( )( )
( ) ( )( )( ) ( ) ( ) ( )( ) ( )
( )
( )
2
23
3
3
2 5 3 1
2 5 2 3 1 3 3 1 2
6 2 5 2 3 1
3 1
6 32
3 1
r x x x
r x x x x
x x
x
x
x
−
−−
= − +
′ = − − + + +
− − + +=
+
− +=+
(c) ( ) ( ) ( ) ( )( )( )( )( )
( )( ) ( )( )
( )
2
4
3
3
3 1 2 2 5 2 3 1 3
3 1
3 1 2 6 2 5
3 1
6 32
3 1
x x xr x
x
x x
x
x
x
+ − − +′ =
+
+ − −=
+
− +=+
(d) Answers will vary.
3
3
2
1
2−2
−2
−3
x
f
y
f ′
x1 2 3−3 −2 −1
−1
−2
−3
1
3
2f
ff ′
f ′
y
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Section 2.4 The Chain Rule 167
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97. (a) ( ) ( ) ( ) ( )2g x f x g x f x′ ′= − =
(b) ( ) ( ) ( ) ( )2 2h x f x h x f x′ ′= =
(c) ( ) ( ) ( ) ( )( ) ( )3 3 3 3 3r x f x r x f x f x′ ′ ′= − = − − = − −
So, you need to know ( )3 .f x′ −
( ) ( ) ( )( )( ) ( ) ( )( )
13
0 3 0 3 1
1 3 3 3 4 12
r f
r f
′ ′= − = − − =
′ ′− = − = − − =
(d) ( ) ( ) ( ) ( )2 2s x f x s x f x′ ′= + = +
So, you need to know ( )2 .f x′ +
( ) ( ) 13
2 0 , etc.s f′ ′− = = −
98. (a) ( ) ( ) ( )( ) ( ) ( ) ( ) ( )( ) ( )( ) ( )( )5 3 2 6 3 24
f x g x h x
f x g x h x g x h x
f
=
′ ′ ′= +
′ = − − + =
(b) ( ) ( )( )( ) ( )( ) ( )( ) ( )( ) ( )5 3 2 2 3
f x g h x
f x g h x h x
f g g
=
′ ′ ′=
′ ′ ′= − = −
Not possible, you need ( )3g′ to find ( )5 .f ′
(c) ( ) ( )( )
( ) ( ) ( ) ( ) ( )( )
( ) ( )( ) ( )( )( )
2
2
3 6 3 2 12 45
9 33
g xf x
h x
h x g x g x h xf x
h x
f
=
′ ′−′ =
− − −
′ = = =
(d) ( ) ( )
( ) ( ) ( )( ) ( ) ( )
3
2
2
3
5 3 3 6 162
f x g x
f x g x g x
f
=
′ ′=
′ = − =
99. (a) ( ) ( )( ) ( ) ( ) ( )( ) ( )( ) ( )( ) ( )( ) ( ) ( ) ( ) ( )( )
12
1 12 2
, 1 4, 1 , 4 1
1 1 1 4 1 1
h x f g x g g f
h x f g x g x
h f g g f g
′ ′= = = − = −
′ ′ ′=
′ ′ ′ ′ ′= = = − − =
(b) ( ) ( )( ) ( ) ( ) ( )( ) ( )( ) ( )( ) ( )( ) ( ) ( )( )
, 5 6, 5 1, 6 does not exist.
5 5 5 6 1
s x g f x f f g
s x g f x f x
s g f f g
′ ′= = = −
′ ′ ′=
′ ′ ′ ′= = −
( )5s′ does not exist because g is not differentiable at 6.
x −2 −1 0 1 2 3
4 −1 −2 −4
4 −1 −2 −4
8 −2 −4 −8
12 1
−1 −2 –4
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168 Chapter 2 Differentiation
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100. (a) ( ) ( )( )( ) ( )( ) ( )( ) ( )( ) ( ) ( )( ) 1
23 3 3 5 1
h x f g x
h x f g x g x
h f g g f
=
′ ′ ′=
′ ′ ′ ′= = =
(b) ( ) ( )( )( ) ( )( ) ( )( ) ( )( ) ( ) ( )( ) ( )( )9 9 9 8 2 1 2 2
s x g f x
s x g f x f x
s g f f g
=
′ ′ ′=
′ ′ ′ ′= = = − = −
101. (a) ( )
( )( )( ) ( )( )
1
2
2
132,400 331
132,4001 132,400 331 1
331
F v
F vv
−
−
= −
′ = − − − =−
When 30, 1.461.v F ′= ≈
(b) ( )
( )( )( ) ( )( )
1
2
2
132,400 331
132,4001 132,400 331 1
331
F v
F vv
−
−
= +
−′ = − + − =+
When 30, 1.016.v F ′= ≈ −
102.
[ ] [ ]
1 13 4
1 13 4
cos 12 sin 12
12 sin 12 12 cos 12
4 sin 12 3 cos 12
y t t
v y t t
t t
= −
′= = − −
= − −
When 8, 0.25 ft and 4 ft/sec.t y vπ= = =
103. 0.2 cos 8tθ =
The maximum angular displacement is 0.2θ = (because 1 cos 8 1).t− ≤ ≤
[ ]0.2 8 sin 8 1.6 sin 8d
t tdt
θ = − = −
When 3, 1.6 sin 24 1.4489t d dtθ= = − ≈ rad/sec.
104. cosy A tω=
(a) Amplitude: 3.5
1.752
1.75 cos
A
y tω
= =
=
Period: 2
1010 5
1.75 cos5
ty
π πω
π
= =
=
(b) 1.75 sin 0.35 sin5 5 5
t tv y
π π ππ ′= = − = −
105. (a) ( ) ( )27.3 sin 0.49 1.90 57.1T t t= − +
(b)
The model is a good fit.
(c) ( ) ( )13.377 cos 0.49 1.90T t t′ = −
(d) The temperature changes most rapidly around spring (March–May) and fall (Oct.–Nov.). The temperature changes most slowly around winter (Dec.–Feb.) and summer (Jun.–Aug.). Yes. Explanations will vary.
106. (a) According to the graph ( ) ( )4 1 .C C′ ′>
(b) Answers will vary.
107. ( )
( )
( ) ( ) ( )( )
2222
3232
3400 1 400 1200 2
2
48002400 2 2
2
N tt
tN t t t
t
−
−
= − = − + +
′ = + =+
(a) ( )0 0N ′ = bacteria/day
(b) ( ) ( )( )3
4800 1 48001 177.8
271 2N ′ = = ≈
+bacteria/day
(c) ( ) ( )( )3
4800 2 96002 44.4
2164 2N ′ = = ≈
+bacteria/day
(d) ( ) ( )( )3
4800 3 14,4003 10.8
13319 2N ′ = = ≈
+bacteria/day
(e) ( ) ( )( )3
4800 4 19,2004 3.3
583216 2N ′ = = ≈
+bacteria/day
(f ) The rate of change of the population is decreasing as .t → ∞
00 13
90
0
20
−20
13
00 13
90
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Section 2.4 The Chain Rule 169
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108. (a)
( )
( ) 1 2
1
0 10,0000 1
10,00010,000 1
1
kV
t
kV k
V tt
−
=+
= = =+
= = ++
(b) ( )( )
( )
3 2
3 2
3 2
1 500010,000 1
2 1
50001 1767.77 dollars/year
2
dVt
dt t
V
− − = − + = +
−′ = ≈ −
(c) ( ) 3 2
5000 50003 625 dollars/year
4 8V
− −′ = = = −
109. ( ) sinf x xβ=
(a) ( )( )( )
( )
2
3
4 4
cos
sin
cos
sin
f x x
f x x
f x x
f x
β β
β β
β β
β β
′ =
′′ = −
′′′ = −
=
(b) ( ) ( ) ( )2 2 2sin sin 0f x f x x xβ β β β β′′ + = − + =
(c) ( ) ( ) ( )( ) ( ) ( )
2 2
12 1 2 1
1 sin
1 cos
kk k
kk k
f x x
f x x
β β
β β+− −
= −
= −
110. (a) Yes, if ( ) ( )f x p f x+ = for all x, then
( ) ( ),f x p f x′ ′+ = which shows that f is
periodic as well.
(b) Yes, if ( ) ( )2 ,g x f x= then ( ) ( )2 2 .g x f x′ ′=
Because f ′ is periodic, so is .g′
111. (a) ( ) ( )( ) ( )( ) ( )( ) ( )1 1 1
r x f g x g x
r f g g
′ ′ ′=
′ ′ ′=
Note that ( )1 4g = and ( ) 5 0 54 .
6 2 4f
−′ = =−
Also, ( )1 0.g′ = So, ( )1 0.r′ =
(b) ( ) ( )( ) ( )( ) ( )( ) ( )4 4 4
s x g f x f x
s g f f
′ ′ ′=
′ ′ ′=
Note that ( ) 5 5 6 4 14 ,
2 2 6 2 2f g
− ′= = = − and
( ) 54 .
4f ′ = So, ( ) 1 5 5
4 .2 4 8
s ′ = =
112. (a) ( ) ( )( ) ( )
2 2sin cos 1 0
2 sin cos 2 cos sin 0
g x x x g x
g x x x x x
′= + = =
′ = + − =
(b)
( ) ( )
2 2tan 1 sec
1
x x
g x f x
+ =
+ =
Taking derivatives of both sides, ( ) ( ).g x f x′ ′=
Equivalently,
( ) 22 sec sec tan 2 sec tan f x x x x x x′ = ⋅ = and
( ) 2 22 tan sec 2 sec tan ,g x x x x x′ = ⋅ = which
are the same.
113. (a) If ( ) ( ),f x f x− = − then
( ) ( )
( )( ) ( )( ) ( )
1
.
− = −
′ ′− − = −′ ′− =
d df x f x
dx dxf x f x
f x f x
So, ( )f x′ is even.
(b) If ( ) ( ),f x f x− = then
( ) ( )
( )( ) ( )( ) ( )
1
.
− =
′ ′− − =′ ′− = −
d df x f x
dx dxf x f x
f x f x
So, f ′ is odd.
114.
( ) ( )
2
1 22 2
2
12
2
, 0
u u
d du u u uu
dx dxuu u
u uuu
−
=
′ = = ′ ′= = ≠
115. ( )
( )
3 5
3 5 53 ,
3 5 3
g x x
xg x x
x
= −
−′ = ≠ −
116. ( )
( )
2
2
2
9
92 , 3
9
f x x
xf x x x
x
= −
− ′ = ≠ ± −
117. ( )
( )
cos
sin cos , 0
h x x x
xh x x x x x
x
=
′ = − + ≠
118. ( )
( )
sin
sincos ,
sin
f x x
xf x x x k
xπ
=
′ = ≠
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170 Chapter 2 Differentiation
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119. (a) ( ) ( )( ) ( )( ) ( )
2
2
tan 4 1
sec 4 2
2 sec tan 4 4
f x x f
f x x f
f x x x f
π
π
π
= =
′ ′= =
′′ ′′= =
(b)
( ) ( )
( ) ( )( ) ( )
( ) ( )
1
22
2
2 4 1
14 4 2 4 1
2
2 4 2 4 1
P x x
P x x x
x x
π
π π
π π
= − +
= − + − +
= − + − +
(c) 2P is a better approximation than 1.P
120. (a) ( ) ( )
( ) ( )
( ) ( ) ( ) ( )2
3 2
2sec 6
3
2sec tan 6
3
10 3sec sec tan sec tan 6
9
sec sec tan
f x x f
f x x x f
f x x x x x x f
x x x
π
π
π
= =
′ ′= =
′′ ′′= + =
= +
( ) ( )
( )
1
2
2
2
2 26
3 3
1 10 2 2
2 6 3 63 3 3
5 2 2
6 3 63 3 3
P x x
P x x x
x x
π
π π
π π
= − +
= ⋅ − + − +
= − + − +
(b)
(c) 2P is a better approximation than 1.P
(d) The accuracy worsens as you move away from 6.x π=
121. True
122. False. ( ) ( ) sin and 0 0f x b x f′ ′= − =
123. True
124. True
125. ( )( )( )
( ) ( ) ( ) ( ) ( )
1 2
1 2
1 2
1 20 0 0
sin sin 2 sin
cos 2 cos 2 cos
0 2
0 sin2 0 lim lim lim 1
0 sin sin
n
n
n
nx x x
f x a x a x a nx
f x a x a x na nx
f a a na
f x f f x f xxa a na f
x x x x→ → →
= + + +
′ = + + +
′ = + + +
−′+ + + = = = ⋅ = ≤
−
0 π2
−1
5
f
P2
P1
(d) The accuracy worsens as you move away from
−1
−1.5 1.5
3
f
P1
P2
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Section 2.5 Implicit Differentiation 171
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126. ( )
( )( ) ( ) ( )( )( )
( )( ) ( ) ( ) ( )
( )
1 1 1
1 2 2 2
1 1 1 1 1
1 1 1
n nk k k k kn n n nn
n n nk k k
x P x P x n x kx x P x n kx P xP xd
dx x x x
+ − −
+ + +
′ ′− − + − − − + = = − − −
( ) ( )
( ) ( ) ( ) ( ) ( ) ( )
( ) ( ) ( )
1
2 11
1
11
1
11 1 1
1
1 1 1
nnkn n k
nnk k kn n nn k
n n
dP x x
dx x
d dP x x x P x n kx P x
dx dx x
P n kP
+
+ −+
+
= − −
′= − = − − + − = − +
For ( )
( )( )
( )1
112 2
11, 1 .
1 1 1
k
k k k
P xd kxn P k
dx x x x
−− = = = = − − − −Also, ( )0 1 1.P =
You now use mathematical induction to verify that ( ) ( )1 !n
nP k n= − for 0.n ≥ Assume true for n. Then
( ) ( ) ( ) ( ) ( ) ( ) ( )11 1 1 1 1 ! 1 !.
n nn nP n k P n k k n k n
++ = − + = − + − = − +
Section 2.5 Implicit Differentiation
1. Answers will vary. Sample answer: In the explicit form of a function, the variable is explicitly written as a function of x. In an implicit equation, the function is only implied by an equation. An example of an implicit
function is 2 5.x xy+ = In explicit form it would be
( )25 .y x x= −
2. Answers will vary. Sample answer: Given an implicit equation, first differentiate both sides with respect to x. Collect all terms involving y′ on the left, and all other
terms to the right. Factor out y′ on the left side. Finally,
divide both sides by the left-hand factor that does not contain .y′
3. You use implicit differentiation to find the derivative y′when it is difficult to express y explicitly as a function
of x.
4. If y is an implicit function of ,x then to compute ,y′ you differentiate the equation with respect to .x For example,
if 2 1,xy = then 2 2 0.y xyy′+ = Here, the derivative of2y is 2 .yy′
5. 2 2 9
2 2 0
x y
x yy
xy
y
+ =′+ =
′ = −
6. 2 2 25
2 2 0
x y
x yy
xy
y
− =′− =
′ =
7. 5 5
4 4
4 4
4
4
16
5 5 0
5 5
x y
x y y
y y x
xy
y
+ =
′+ =
′ = −
′ = −
8. 3 3
2 2
2 2
2 2
2 2
2 3 64
6 9 0
9 6
6 2
9 3
x y
x y y
y y x
x xy
y y
+ =
′+ =
′ = −
−′ = = −
9.
( )
3 2
2
2
2
7
3 2 0
2 3
3
2
x xy y
x xy y yy
y x y y x
y xy
y x
− + =
′ ′− − + =
′− = −
−′ =−
10.
( ) ( )( )
( )
2 2
2 2
2 2
2
2 2 0
2 2
2
2
x y y x
x y xy y yxy
x xy y y xy
y y xy
x x y
+ = −
′ ′+ + + =
′+ = − +
− +′ =
+
11.
( )
3 3
3 2 2 3
3 2 2 3
2 3
3 2
0
3 3 1 0
3 1 1 3
1 3
3 1
x y y x
x y y x y y
x y y x y
x yy
x y
− − =
′ ′+ − − =
′− = −
−′ =−
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172 Chapter 2 Differentiation
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12.
( ) ( )
2
1 2 2
2
2
2
2
1
12
2
22 2
22 2
22
2
4
2
xy x y
xy xy y xy x y
x yy xy x y
xy xy
x yx y xy
xy xy
yxy
xyy
xx
xy
xy xy yy
x x xy
−
= +
′ ′+ = +
′ ′+ = +
′− = −
−′ =
−
−′ =−
13.
( )
3 2 2
2 2 2
2 2 2
2 2
2
3 2 12
3 3 6 4 2 0
4 3 6 3 2
6 3 2
4 3
x x y xy
x x y xy xyy y
xy x y xy x y
xy x yy
xy x
− + =
′ ′− − + + =
′− = − −
− −′ =−
14.
( )
4 2
4 3 2
4 3 2
3 2
4
8 3 9
4 8 8 6 3 0
8 6 8 4 3
8 4 3
8 6
x y xy xy
x y x y xy y xyy y
x x xy y y x y y
y x y yy
x x xy
− + =
′ ′ ′+ − − + + =
′− + = − −
− −′ =− +
15.
( )sin 2 cos 2 1
cos 4 sin 2 0
cos
4 sin 2
x y
x y y
xy
y
+ =′− =
′ =
16. ( )( ) ( )
( )
2sin cos 2
2 sin cos cos sin 0
cos sin 0
cos
sin
x y
x y x y y
x y y
xy
y
π π
π π π π π π
π π π πππ
+ =
′+ − = ′− =
′ =
17. ( )( ) ( )2
2
csc 1 tan
csc cot 1 tan sec
csc cot 1 tan
sec
x x y
x x y x y y
x x yy
x y
= +
′− = + +
+ +′ = −
18.
( )2
22 2
cot
csc 1
1 1tan
1 csc cot
y x y
y y y
y yy y
= −
′ ′− = −
′ = = = −− −
19.
[ ] ( )( ) ( )
( )( )
sin
cos
cos cos
cos
1 cos
y xy
y xy y xy
y x xy y y xy
y xyy
x xy
=′ ′= +
′ ′− =
′ =−
20.
( ) ( )
2
22
1sec
1 11 sec tan
1 1cos cot
sec 1 tan 1
xy
y
y y y
yy y
y y y y
=
′= −
−′ = = −
21. (a) 2 2
2 2
2
64
64
64
x y
y x
y x
+ =
= −
= ± −
(b)
(c) Explicitly:
( ) ( )1 22
2
2
164 2
2 64
64
−= ± − − =
−−= = −
± −
dy xx x
dx x
x x
yx
(d) Implicitly: 2 2 0x yy
xy
y
′+ =
′ = −
y1 = 64 − x2
−12 −4 4 12
12
4
−12 y2 = − 64 − x2
y
x
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Section 2.5 Implicit Differentiation 173
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22. (a)
( )( )
2 2
2 2 2
2 2
2
25 36 300
36 300 25 25 12
2512
36
512
6
x y
y x x
y x
y x
+ =
= − = −
= −
= ± −
(b)
(c) Explicitly:
( ) ( )1 22
2
5 112 2
6 2
5
6 12
25
36
dyx x
dx
x
x
x
y
− = ± − −
=−
= −
(d) Implicitly: 50 72 0
50 25
72 36
x y y
x xy
y y
′+ ⋅ =−′ = = −
23. (a) 2 2
2 2
2 22
2
16 16
16 16
161
16 16
16
4
y x
y x
x xy
xy
− =
= +
+= + =
± +=
(b)
(c) Explicitly:
( ) ( )
( )
1 22
2
116 2
24
4 4 164 16
−± + −
=
± ±= = =±+
x xdy
dxx x x
y yx
(d) Implicitly: 2 216 16
32 2 0
32 2
2
32 16
y x
yy x
yy x
x xy
y y
− =′ − =
′ =
′ = =
24. (a)
( ) ( )( ) ( )
( ) ( )
( )
( )
2 2
2 2
2 2
2 2
2
2
4 6 9 0
4 4 6 9 9 4 9
2 3 4
3 4 2
3 4 2
3 4 2
x y x y
x x y y
x y
y x
y x
y x
+ − + + =
− + + + + = − + +
− + + =
+ = − −
+ = ± − −
= − ± − −
(b)
(c) Explicitly: (d) Implicitly:
( ) ( )
( )
1 22
2
14 2 2 2
22
4 2
2
3
dyx x
dxx
x
x
y
− = ± − − − −
−=− −
−= −+
( ) ( )( )
( )
2 2 4 6 0
2 6 2 4
2 6 2 2
2 2 2
2 3 3
x yy y
yy y x
y y x
x xy
y y
′ ′+ − + =′ ′+ = − +
′ + = − −
− − −′ = = −+ +
y1 = 12 − x2
y2 = − 12 − x2
y
x−2−4−6 2 4 6
−2
−4
−6
2
4
6
56
56
y1 = x2 + 1614
y2 = − x2 + 1614
−6 6−2
−4
−6
2
4
6
y
x
y2 = −3 − 4 − (x − 2)2
y
x−1 1 2 3 4 5 6−1
−2
−3
−4
−5
−6
1 y1 = −3 + 4 − (x − 2)2
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25.
( )6
1 0
=′ + =
′ = −
′ = −
xy
xy y
xy y
yy
x
At ( ) 16, 1 :
6y′− − = −
26. 3
3
2 3
3 2
2
3
3 6
2
3 0
3
3 3
=
=′+ =′ = −
−′ = = −
x y
x y
x y x y
x y x y
x y yy
x x
At ( ) ( )3 21, 2 : 6
1y
−′ = = −
27.
( )( ) ( )( )( )
( )
( )
22
2
2 2
22
22
22
49
49
49 2 49 22
49
1962
49
98
49
−=++ − −
′ =+
′ =+
′ =+
xy
x
x x x xyy
x
xyy
x
xy
y x
At ( )7, 0 : y′ is undefined.
28.
( )( ) ( )( )( )
( )
23
3
3 2 22
23
2 4
22 3
364
36
36 2 36 312
36
72 108
12 36
−=++ − −
′ =+
+ −′ =+
xy
x
x x x xy y
x
x x xy
y x
At ( )6, 0 : y′ is undefined (division by 0).
29. ( )
( ) ( )( )( )
3 3 3
3 2 2 3 3 3
2 2
2 2
2 2
2 2
3 3
3 3 0
0
2 2 0
2 2
2
2
+ = +
+ + + = +
+ =+ =
′ ′+ + + =
′+ = − +
+′ = −
+
x y x y
x x y xy y x y
x y xy
x y xy
x y xy xyy y
x xy y y xy
y y xy
x x y
At ( )1, 1 : 1y′− = −
30.
( )
3 3
2 2
2 2
2
2
6 1
3 3 6 6
3 6 6 3
6 3
3 6
x y xy
x y y xy y
y x y y x
y xy
y x
+ = −
′ ′+ = +
′− = −
−′ =−
At ( ) 18 12 6 22, 3 :
27 12 15 5y
−′ = = =−
31. ( )( ) ( )
( )( )( )
( )( )
2
2
2
2
2
2
2
2
tan
1 sec 1
1 sec
sec
tan
tan 1
sin
1
x y x
y x y
x yy
x y
x y
x y
x y
x
x
+ =
′+ + =
− +′ =
+
− +=
+ +
= − +
= −+
At ( )0, 0 : 0y′ =
32.
[ ]cos 1
sin cos 0
cos
sin
1cot
cot
x y
x y y y
yy
x y
yx
y
x
=′− + =
′ =
=
=
At 1
2, :3 2 3
yπ ′ =
33. ( )( ) ( )
( )
( )
2
2
2
2
2
22
4 8
4 2 0
2
4
2 8 4
416
4
x y
x y y x
xyy
x
x x
xx
x
+ =
′+ + =
−′ =+ − + =
+−=
+
At ( ) 32 12, 1 :
64 2y
−′ = = −
2
8Or, you could just solve for :
4y y
x = +
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Section 2.5 Implicit Differentiation 175
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34. ( )( )( ) ( )
( )
2 3
2 2
2 2
4
4 2 1 3
3
2 4
x y x
x yy y x
x yy
y x
− =
′− + − =
+′ =−
At ( )2, 2 : 2y′ =
35. ( )( )( ) ( )
( ) ( )
22 2 2
2 2 2
3 2 2 3 2
2 3 2 3 2
2 3 2 3 2
3 2
2 3 2
4
2 2 2 4 8
4 4 4 4 4 8
4 4 4 8 4 4
4 4 2
2
x y x y
x y x yy x y y x
x x yy xy y y x y xy
x yy y y x y xy x xy
y x y y x xy x xy
xy x xyy
x y y x
+ =
′ ′+ + = +
′ ′ ′+ + + = +
′ ′ ′+ − = − −
′ + − = − −
− −′ =+ −
At ( )1, 1 : 0y′ =
36.
( )
3 3
2 2
2 2
2 2
2 2
6 0
3 3 6 6 0
3 6 6 3
6 3 2
3 6 2
x y xy
x y y xy y
y y x y x
y x y xy
y x y x
+ − =
′ ′+ − − =
′ − = −
− −′ = =− −
At ( ) ( )( ) ( )16 3 16 94 8 32 4
, :3 3 64 9 8 3 40 5
y− ′ = = = −
37. ( ) ( ) ( )( )
23 4 5 , 6, 1
2 3 4
2
3
y x
y y
yy
− = −
′− =
′ =−
At ( ) 26, 1 : 1
1 3y′ = = −
−
Tangent line: ( )1 1 6
7
y x
y x
− = − −
= − +
38. ( ) ( ) ( )( ) ( )
( ) ( )( )
2 22 3 37, 4, 4
2 2 2 3 0
3 2
2
3
x y
x y y
y y x
xy
y
+ + − =
′+ + − =
′− = − +
+′ = −
−
At ( ) 64, 4 : 6
1y′ = − = −
Tangent line: ( )4 6 4
6 28
y x
y x
− = − −
= − +
39. ( )2 2 2 2
2 2
2
2
9 4 0, 4, 2 3
2 2 18 8 0
18 2
2 8
x y x y
x yy xy x yy
x xyy
x y y
− − = −
′ ′+ − − =
−′ =−
At ( ) ( ) ( )( )( )( )18 4 2 4 12
4, 2 3 :2 16 2 3 16 3
24 1 3
648 3 2 3
y− − −
′− =−
= = =
Tangent line: ( )32 3 4
6
3 83
6 3
y x
y x
− = +
= +
40. ( )2 3 2 3
1 3 1 3
1 31 3
1 3
5, 8, 1
2 20
3 3
x y
x y y
x yy
y x
− −
−
−
+ =
′+ =
− ′ = = −
At ( ) 18, 1 :
2y′ = −
Tangent line: ( )11 8
21
52
y x
y x
− = − −
= − +
41. ( ) ( ) ( )
( )( ) ( )
22 2 2 2
2 2
3 100 , 4, 2
6 2 2 100 2 2
x y x y
x y x yy x yy
+ = −
′ ′+ + = −
( )( )( ) ( )
211
At 4, 2 :
6 16 4 8 4 100 8 4
960 480 800 400
880 160
y y
y y
y
y
′ ′+ + = −
′ ′+ = −′ = −
′ = −
Tangent line: ( )211
30211 11
2 4
11 2 30 0
y x
y x
y x
− = − −
+ − =
= − +
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42. ( ) ( )2 2 2 2
2 2 4 2
2 2 3
2 , 1, 1
2
2 2 4 4
y x y x
y x y x
yy x xy y y x
+ =
+ =
′ ′+ + =
( )
13
At 1, 1 :
2 2 4 4
6 2
y y
y
y
′ ′+ + =′ =
′ =
Tangent line: ( )13
1 23 3
1 1y x
y x
− = −
= +
43. Answers will vary. Sample answers:
22
2 2
2
22
22
4
2
xy yx
xyx x y
x
x y
xy y
= =
−+ = =
+ =
+ =
44. The equation 2 2 2 1x y+ + = implies 2 2 1,x y+ = −which has no real solutions.
45. (a) ( )2 2
1, 1, 22 8
04
4
x y
yyx
xy
y
+ =
′+ =
′ = −
At ( )1, 2 : 2y′ = −
Tangent line: ( )2 2 1
2 4
y x
y x
− = − −
= − +
(b)
( ) ( )
2 2 2
2 2 2 2 2
20
0 0 0 020
2 20 0 0 02 2 2 2
2 21 0
, Tangent line at ,
′ −′+ = + = =
−− = −
−− = +
x y x yy b xy
a b a b a y
b xy y x x x y
a y
y y y x x x
b b a a
Because2 20 02 2
1,x y
a b+ = you have 0 0
2 21.
y y x x
b a+ =
Note: From part (a),
( ) ( )1 2 1 1
1 1 2 4,2 8 4 2
x yy x y x+ = = − + = − +
Tangent line.
46. (a) ( )2 2
1, 3, 26 8
03 4
4 34
3
x y
x yy
y xy
xy
y
− = −
′− =
′ =
′ =
At ( ) ( )( )4 3
3, 2 : 23 2
y′− = = −−
Tangent line: ( )2 2 3
2 4
y x
y x
+ = − −
= − +
(b)
( ) ( )
2 2 2
2 2 2 2 2
20
0 0 0 020
2 20 0 0 0
2 2 2 2
2 21 0
, Tangent line at ,
′ ′− = − = =
− = −
− = −
x y x yy xby
a b a b ya
x by y x x x y
y a
yy y x x x
b b a a
Because2 20 02 2
1,x y
a b− = you have 0 0
2 21.
x x yy
a b− =
Note: From part (a),
( )23 1
1 1 2 4,6 8 2 4
yx yx y x
−− = + = = − +
Tangent line.
47. 2
22
2 2 2
2
tan
sec 1
1cos ,
sec 2 2
sec 1 tan 1
1
1
y x
y y
y y yy
y y x
yx
π π
=
′ =
′ = = − < <
= + = +
′ =+
48.
2 2
2 2
2 2
2
cos
sin 1
1, 0
sin
sin cos 1
sin 1 cos
sin 1 cos 1
1, 1 1
1
y x
y y
y yy
y y
y y
y y x
y xx
π
=′− ⋅ =
−′ = < <
+ =
= −
= − = −
−′ = − < <−
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Section 2.5 Implicit Differentiation 177
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49.
( )
( )
2 2
2
2
2 2
3
3
4
2 2 0
1
4
x y
x yy
xy
y
y xyy
y
y x x y
y
y x
y
y
+ =′+ =
−′ =
′− +′′ =
− + −=
− −=
= −
50.
( )
2
2
2
2
22
4 2
4 2 2
4 2
3
4 5
2 4 0
4 2
2 2 2 0
4 24 2 0
4 4 2 2 0
16 8 2 0
6 16
6 16
x y x
x y xy
xyy
x
x y xy xy y
xyx y x y
x
x y x xy x y
x y x x y x y
x y x y x
xyy
x
− =′ + − =
−′ =
′′ ′ ′+ + + =− ′′ + + =
′′ + − + =
′′ + − + =′′ = −
−′′ =
51.
( )
( )( )
( )( )
( )( ) ( )
2
2
2
2
2
22
22 2
2 2 2
2 22 2
2 5
2 5
1 5 2
5 2
1
2 1 2 2
5 21 2 4 2 4
1
4 5 22
1 1
2 1 20 8 6 20 2
1 1
− = +
′ ′+ = +
′− = −
−′ =−
′ ′′ ′+ − = − −
− ′′ ′− = − − = − − − −−′′ = −
− −
− − − + − += =− −
x y x y
xy x y y
x y xy
xyy
x
xy x y y xy
xyx y y xy y x
x
x xyyy
x x
y x x x y x y x y
x x
52.
( )
( )( )
( ) ( )
( ) ( ) ( )( )
( )( )( )
( )
2
2
2
22
3 3
2
1 2
2 2
2 2
2 2
2
2
2 2
2 2 2
2 22 2 2 2 2
2 2
2 2 2 2 2 2 2
2 2
2 4 2 2 2
− = +′ ′+ = +
′ ′− = −′− = −
−′ =−
′′ ′ ′ ′′ ′+ + = +
′′ ′′ ′ ′− = −
− −′′ ′ ′− = − = − − − − − − − − − + ′′ = =
− −
− + − + −=
xy x y
xy y yy
xy yy y
x y y y
yy
x y
xy y y yy y
xy yy y y
y yx y y y y
x y x y
y y x y y x yy
x y x y
x y y xy y
x( )( )
( )( )
( ) ( )
2
3 3
3 3
2 2 4
2 2
2 5 10
2 2
− + −=
− −
−= =
− −
y xy x
y y x
y x x y
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178 Chapter 2 Differentiation
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53.
2
2
7 sin 2
7 7 cos 0
7 cos
77 7 7 sin 0
7 cos7 sin 14 sin 14
7
14 2 cos7 sin
sin 14 2 cos
7 7sin 14 2 cos
7
xy x
xy y x
y xy
xxy y y x
y xxy x y x
x
y xxy x
xx y x
yx x
x x y xy
x
+ =′ + + =
− −′ =
′′ ′ ′+ + − =
− − ′′ ′= − = −
+′′ = +
+′′ = +
+ +′′ =
54.
2
3 4 cos 6
3 3 4 sin 0
4 sin 3
33 3 3 4 cos 0
4 sin 33 6 4 cos 6 4 cos
3
8 sin 6 4 cos
8 sin 6 4 cos
3
xy x
xy y x
x yy
xxy y y x
x yxy y x x
x
x y x x
xx y x x
yx
− = −′ + + =
− −′ =
′′ ′ ′+ + + =
− − ′′ ′= − − = − −
+ −=
+ −′′ =
55.
1 2 1 2
5
1 10
2 2
x y
x y y
yy
x
− −
+ =
′+ =
−′ =
At ( ) 29, 4 :
3y′ = −
Tangent line: ( )24 9
32 3 30 0
y x
x y
− = − −
+ − =
56.
( )( ) ( )( )( ) ( )
( )
22
2 2 2
2 22 2
2
22
1
1
1 1 1 2 1 2 22
1 1
1 2
2 1
xy
x
x x x x x xyy
x x
x xy
y x
−=++ − − + − +′ = =
+ +
+ −′ =+
At( ) ( )2
5 1 4 4 12, :
5 10 52 54 1
5
y + −′ = =
+
Tangent line: ( )5 12
5 10 5
10 5 10 2
10 5 8 0
y x
y x
x y
− = −
− = −
− + =
−1
−1 14
9
(9, 4)
−1
−1 5
55
2,( )1
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Section 2.5 Implicit Differentiation 179
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57. 2 2 25
2 2 0
x y
x yy
xy
y
+ =′+ =
−′ =
At ( )4, 3 :
Tangent line:
( )43 4 4 3 25 0
3y x x y
−− = − + − =
Normal line: ( )33 4 3 4 0
4y x x y− = − − =
At ( )3, 4 :−
Tangent line:
( )34 3 3 4 25 0
4y x x y− = + − + =
Normal line: ( )44 3 4 3 0
3y x x y
−− = + + =
58. 2 2 36
2 2 0
x y
x yy
xy
y
+ =′+ =
′ = −
At ( )6, 0 ; slope is undefined.
Tangent line: 6x =
Normal line: 0y =
At ( )5, 11 , slope is 5
.11
−
Tangent line: ( )511 5
11
11 11 5 25
5 11 36 0
y x
y x
x y
−− = −
− = − +
+ − =
Normal line: ( )1111 5
5
5 5 11 11 5 11
5 11 0
y x
y x
y x
− = −
− = −
− =
59. 2 2 2
2 2 0
slope of tangent line
slope of normal line
x y r
x yy
xy
y
y
x
+ =′+ =
−′ = =
=
Let ( )0 0,x y be a point on the circle. If 0 0,x = then the tangent line is horizontal, the normal line is vertical and, hence, passes
through the origin. If 0 0,x ≠ then the equation of the normal line is
( )00 0
0
0
0
yy y x x
x
yy x
x
− = −
=
which passes through the origin.
−6
6
−9 9
(4, 3)
−6
−9 9
(−3, 4)
6
−12 12
−8
8
(6, 0)
−12 12
−8
(5, 11)
8
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180 Chapter 2 Differentiation
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60.
( )
2 4
2 4
21 at 1, 2
y x
yy
yy
=′ =
′ = =
Equation of normal line at ( )1, 2 is
( )2 1 1 , 3 .y x y x− = − − = − The centers of the
circles must be on the normal line and at a distance of
4 units from ( )1, 2 . Therefore,
( ) ( )( )
22
2
1 3 2 16
2 1 16
1 2 2.
x x
x
x
− + − − =
− =
= ±
Centers of the circles: ( )1 2 2, 2 2 2+ − and
( )1 2 2, 2 2 2− +
Equations: ( ) ( )( ) ( )
2 2
2 2
1 2 2 2 2 2 16
1 2 2 2 2 2 16
x y
x y
− − + − + =
− + + − − =
61. 2 225 16 200 160 400 0
50 32 200 160 0
200 50
160 32
x y x y
x yy y
xy
y
+ + − + =′ ′+ + − =
+′ =−
Horizontal tangents occur when 4:x = −
( ) ( )
( )
225 16 16 200 4 160 400 0
10 0 0,10
y y
y y y
+ + − − + =
− = =
Horizontal tangents: ( ) ( )4, 0 , 4, 10− −
Vertical tangents occur when 5:y =
( )
225 400 200 800 400 0
25 8 0 0, 8
x x
x x x
+ + − + =
+ = = −
Vertical tangents: ( ) ( )0, 5 , 8, 5−
62. 2 24 8 4 4 0
8 2 8 4 0
8 8 4 4
2 4 2
x y x y
x yy y
x xy
y y
+ − + + =′ ′+ − + =
− −′ = =+ +
Horizontal tangents occur when 1:x =
( ) ( )
( )
2 2
2
4 1 8 1 4 4 0
4 4 0 0, 4
y y
y y y y y
+ − + + =
+ = + = = −
Horizontal tangents: ( ) ( )1, 0 , 1, 4−
Vertical tangents occur when 2:y = −
( ) ( )
( )
22
2
4 2 8 4 2 4 0
4 8 4 2 0 0, 2
x x
x x x x x
+ − − + − + =
− = − = =
Vertical tangents: ( ) ( )0, 2 , 2, 2− −
x2−4−8 −6−10
−2
10
6
4(0, 5)
(−4, 10)
(−4, 0)
(−8, 5)
y
x1 2 3 4−1
−1
−3
−4
−5
(1, −4)
(2, −2)
(1, 0)
(0, −2)
y
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Section 2.5 Implicit Differentiation 181
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63. Find the points of intersection by letting 2 4y x= in the equation 2 22 6.x y+ =
( )( )22 4 6 and 3 1 0x x x x+ = + − =
The curves intersect at ( )1, 2 .±
: :
4 2 0 2 4
2 2
Ellipse Parabola
x yy yy
xy y
y y
′ ′+ = =
′ ′= − =
At ( )1, 2 , the slopes are:
1 1y y′ ′= − =
At ( )1, 2 ,− the slopes are:
1 1y y′ ′= = −
Tangents are perpendicular.
64. Find the points of intersection by letting 2 3y x= in the equation 2 22 3 5.x y+ =
2 3 3 22 3 5 and 3 2 5 0x x x x+ = + − =
Intersect when 1.x =
Points of intersection: ( )1, 1±
2 3 2 2
2
2
: 2 3 5:
2 3 4 6 0
3 2
2 3
y x x y
yy x x yy
x xy y
y y
= + =
′ ′= + =
′ ′= = −
At ( )1, 1 , the slopes are:
3 2
2 3y y′ ′= = −
At ( )1, 1 ,− the slopes are:
3 2
2 3y y′ ′= − =
Tangents are perpendicular.
65. and siny x x y= − =
Point of intersection: ( )0, 0
: sin :
1 1 cos
sec
y x x y
y y y
y y
= − =
′ ′= − =′ =
At ( )0, 0 , the slopes are:
1 1y y′ ′= − =
Tangents are perpendicular.
−6 6
−4
y2 = 4x4
(1, −2)
(1, 2)
2x2 + y2 = 6
(1, 1)
(1, −1)
−2
2
4−2
2x2 + 3y2 = 5
y2 = x3
−6 6
−4
(0, 0)
4
x = sin y
x + y = 0
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182 Chapter 2 Differentiation
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66. Rewriting each equation and differentiating:
( ) ( )3
3
22
3 1 3 29 3
1 31 29
3 3
1
= − − =
= + = +
′ ′= = −
x y x y
xy y
x
y x yx
For each value of x, the derivatives are negative reciprocals of each other. So, the tangent lines are orthogonal at both points of intersection.
67. 2 2
0 2 2 0
xy C x y K
xy y x yy
y xy y
x y
= − =′ ′+ = − =
′ ′= − =
At any point of intersection ( ),x y the product of the
slopes is ( )( ) 1.y x x y− = − The curves are orthogonal.
68. 2 2 2
2 2 0
x y C y Kx
x yy y K
xy
y
+ = =′ ′+ = =
′ = −
At the point of intersection ( ), ,x y the product of the
slopes is ( )( ) ( )( ) 1.x y K x Kx K− = − = − The curves
are orthogonal.
69.
Use starting point B.
70. (a) The slope is greater at 3.x = −
(b) The graph has vertical tangent lines at about ( ) ( )2, 3 and 2, 3 .−
(c) The graph has a horizontal tangent line at about ( )0, 6 .
71. (a) ( )4 2 2
2 2 4
2 2 4
2 4
4 4
4 16
14
4
14
4
x x y
y x x
y x x
y x x
= −
= −
= −
= ± −
15
−3
−15 12
x3 = 3y − 3x(3y − 29) = 3
−2
−3 3C = 1
K = −1
2
−3 3
−2
C = 2
K = 1
2
−3 3
−2
C = 1K = −1
2
−2
−3 3
C = 4
K = 2
2
10−10
−10
10
A
B
1800
1800
1994
1671
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Section 2.5 Implicit Differentiation 183
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(b) 2 413 9 4
4y x x= = −
2 4
4 2
2
36 16
16 36 0
16 256 1448 28
2
x x
x x
x
= −
− + =
± −= = ±
Note that ( )22 8 28 8 2 7 1 7 .x = ± = ± = ± So, there are four values of x:
1 7, 1 7, 1 7, 1 7− − − − + +
To find the slope, ( )
( )2
38
2 8 .2 3
x xyy x x y
−′ ′= − =
For ( )11 7, 7 7 ,
3x y′= − − = + and the line is
( )( ) ( )11 1
7 7 1 7 3 7 7 8 7 23 .3 3
y x x = + + + + = + + +
For ( )11 7, 7 7 ,
3x y′= − = − and the line is
( )( ) ( )21 1
7 7 1 7 3 7 7 23 8 7 .3 3
y x x = − − + + = − + −
For ( )11 7, 7 7 ,
3x y′= − + = − − and the line is
( )( ) ( ) ( )31 1
7 7 1 7 3 7 7 23 8 7 .3 3
y x x = − − + − + = − − − −
For ( )11 7, 7 7 ,
3x y′= + = − + and the line is
( )( ) ( ) ( )41 1
7 7 1 7 3 7 7 8 7 23 .3 3
y x x = − + − − + = − + − +
(c) Equating 3y and 4:y
( )( ) ( )( )( )( ) ( )( )
1 17 7 1 7 3 7 7 1 7 3
3 3
7 7 1 7 7 7 1 7
7 7 7 7 7 7 7 7 7 7 7 7 7 7
16 7 14
8 7
7
x x
x x
x x x x
x
x
− − + − + = − + − − +
− + − = + − −
+ − − − + = − − + − −
=
=
If 8 7
,7
x = then 5y = and the lines intersect at8 7
, 5 .7
10−10
−10
y1y3 y2
y4
10
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184 Chapter 2 Differentiation
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72.
1 10
2 2
x y c
dy
dxx y
ydy
dx x
+ =
+ =
= −
Tangent line at ( ) ( )00 0 0 0
0
, :y
x y y y x xx
− = − −
x-intercept: ( )0 0 0 , 0x x y+
y-intercept: ( )0 0 00, y x y+
Sum of intercepts:
( ) ( ) ( ) ( )2 2
0 0 0 0 0 0 0 0 0 0 0 02x x y y x y x x y y x y c c+ + + = + + = + = =
73.
1 1
1 1
1
11
; , integers and 0p q
q p
q p
p p
q q
pp q p q
p
y x p q q
y x
qy y px
p x p x yy
q y q y
p x px x
q x q
− −
− −
−
−−
= >
=
′ =
′ = ⋅ = ⋅
= ⋅ =
So, if 1, , then .n ny x n p q y nx −′= = =
74. 2 2
2 2
2
3100, slope
42 2 0
3 4
4 3
16100
9
25100
96
x y
x yy
xy y x
y
x x
x
x
+ = =
′+ =
′ = − = = −
+ =
=
= ±
( ) ( )Points: 6, 8 and 6, 8− −
75. ( )
( )
2 2
2
1, 4, 04 9
2 20
4 99
4
9 0
4 4
9 4 4
+ =
′+ =
−′ =
− −=−
− − =
x y
x yy
xy
y
x y
y x
x x y
But, 2 2 2 29 4 36 4 36 9 .x y y x+ = = − So, 2 2 29 36 4 36 9 1.x x y x x− + = = − =
Points on ellipse: 3
1, 32
±
( )
3 9 9 3At 1, 3 :
2 4 24 3 2 3
3 3At 1, 3 :
2 2
− − ′ = = = −
′− =
xy
y
y
Tangent lines: ( )
( )
3 34 2 3
2 2
3 34 2 3
2 2
y x x
y x x
= − − = − +
= − = −
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Section 2.6 Related Rates 185
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76. 2
1 2
1, slope of tangent line
2
x y
yy
yy
=′=
′ =
Consider the slope of the normal line joining ( )0, 0x and
( ) ( )2, ,x y y y= on the parabola.
20
20
20
02
1
21
2
yy
y x
y x
y x
−− =−
− = −
= −
(a) If 014,x = then 2 1 1 1
4 2 4,y = − = − which is
impossible. So, the only normal line is the x-axis
( )0 .y =
(b) If 012,x = then 2 0 0.y y= = Same as part (a).
(c) If 0 1,x = then 2 12
y x= = and there are three
normal lines.
The x-axis, the line joining ( )0, 0x and 1 1
, ,2 2
and the line joining ( )0, 0x and 1 1
,2 2
−
(d) If two normals are perpendicular, then their slopes are –1 and 1. So,
( )
20
0 00
0 12 1
2
and
1 2 1 1 31 .
1 4 4 2 4
yy y
y x
x xx
−− = − = =−
= − − = − =−
The perpendicular normal lines are 3
4y x= − +
and 3
.4
y x= −
77. (a) 2 2
132 8
2 20
32 8 4
x y
x yy xy
y
+ =
′ −′+ = =
(b)
At ( ) ( )4 1
4, 2 :4 2 2
y−′ = = −
Slope of normal line is 2.
( )2 2 4
2 6
y x
y x
− = −
= −
(c) ( )
( )
( )( )
22
2 2
2
2 61
32 8
4 4 24 36 32
17 96 112 0
2817 28 4 0 4,
17
xx
x x x
x x
x x x
−+ =
+ − + =
− + =
− − = =
Second point: 28 46
,17 17 −
Section 2.6 Related Rates
1. A related-rate equation is an equation that relates the rates of change of various quantities.
2. Answers will vary. See page 153.
3.
1
2
2
y x
dy dx
dt dtx
dx dyx
dt dt
=
=
=
(a) When 4x = and 3:dx dt =
( )1 33
42 4
dy
dt= =
(b) When 25x = and 2:dy dt =
( )2 25 2 20dx
dt= =
4
6
−4
−6
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4.
( )
23 5
6 5
1
6 5
y x x
dy dxx
dt dtdx dy
dt x dt
= −
= −
=−
(a) When 3x = and 2:dx
dt=
( )6 3 5 2 26dy
dt= − =
(b) When 2x = and 4:dy
dt=
( ) ( )1 4
46 2 5 7
dx
dt= =
−
5. 4
0
xy
dy dxx y
dt dt
dy y dx
dt x dt
dx x dy
dt y dt
=
+ =
= −
= −
(a) When 8, 1/2,x y= = and 10:dx dt =
( )1/2 510
8 8
dy
dt= − = −
(b) When 1, 4,x y= = and 6:dy dt = −
( )1 36
4 2
dx
dt= − − =
6. 2 2 25
2 2 0
x y
dx dyx y
dt dt
dy x dx
dt y dt
dx y dy
dt x dt
+ =
+ =
= −
= −
(a) When 3, 4,x y= = and 8:dx dt =
( )38 6
4
dy
dt= − = −
(b) When 4, 3,x y= = and 2:dy dt = −
( )3 32
4 2
dx
dt= − − =
7. 22 1
2
4
y x
dx
dtdy dx
xdt dt
= +
=
=
(a) When 1:x = −
( )( )4 1 2 8 cm/secdy
dt= − = −
(b) When 0:x =
( )( )4 0 2 0 cm/secdy
dt= =
(c) When 1:x =
( )( )4 1 2 8 cm/secdy
dt= =
8.
( )
( )( )
( )
2
22
2 22 2
1, 6
12
1
2 126
1 1
dxy
x dtdy x dx
dt dtx
x x
x x
= =+−= ⋅+
− −= =+ +
(a) When 2:x = −
( )( )
( )22
12 2 24
251 2
dy
dt
− −= =
+ −
in./sec
(b) When 0:x =
( )
( )2
12 00
1 0
dy
dt
−= =
+ in./sec
(c) When 2:x =
( )( )( )22
12 2 24 in./sec
251 2
dy
dt
−= = −
+
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Section 2.6 Related Rates 187
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9.
( )2 2 2
tan , 3
sec sec 3 3 sec
dxy x
dtdy dx
x x xdt dt
= =
= ⋅ = =
(a) When :3
xπ= −
( )223 sec 3 2 12 ft/sec3
dy
dt
π = − = =
(b) When :4
xπ= −
( )223 sec 3 2 6 ft/sec
4
dy
dt
π = − = =
(c) When 0:x =
( )23 sec 0 3 ft/secdy
dt= =
10.
( )
cos , 4
sin sin 4 4 sin
dxy x
dtdy dx
x x xdt dt
= =
= − ⋅ = − = −
(a) When :6
xπ=
1
4 sin 4 2 cm/sec6 2
dy
dt
π = − = − = −
(b) When :4
xπ=
2
4 sin 4 2 2 cm/sec4 2
dy
dt
π = − = − = −
(c) When :3
xπ=
3
4 sin 4 2 3 cm/sec3 2
dy
dt
π = − = − = −
11. 2
4
2
A r
dr
dtdA dr
rdt dt
π
π
=
=
=
When ( )( ) 237, 2 37 4 296 cm min.dA
rdt
π π= = =
12.
( )
2 3
4
13
3 32
4 2
=
=
= =
sA
ds
dt
dA ds s dss
dt dt dt
When ( )( ) 23 533 341, 41 13 ft hr.
2 2
dAs
dt= = =
13. 3
2
4
3
3
4
V r
dr
dtdV dr
rdt dt
π
π
=
=
=
(a) When 9,r =
( ) ( )2 34 9 3 972 in. /min.dV
dtπ π= =
When 36,r =
( ) ( )2 34 36 3 15,552 in. /min.dV
dtπ π= =
(b) If dr dt is constant, dV dt is proportional to 2.r
14. 3 24, 4
3
800
dV drV r r
dt dtdV
dt
π π= =
=
(a) 24
dr dV dt
dt rπ=
At ( )2
800 230, cm min.
94 30
drr
dt ππ= = =
At ( )2
800 885, cm min.
2894 85
drr
dt ππ= = =
(b) dr
dtdepends on 2,r not .r
15. 3
2
6
3
V x
dx
dtdV dx
xdt dt
=
=
=
(a) When 2,x =
( ) ( )2 33 2 6 72 cm /sec.dV
dt= =
(b) When 10,x =
( ) ( )2 33 10 6 1800 cm /sec.dV
dt= =
16. 26
6
12
s x
dx
dtds dx
xdt dt
=
=
=
(a) When 2,x =
( )( ) 212 2 6 144 cm /sec.ds
dt= =
(b) When 10,x =
( )( ) 212 10 6 720 cm /sec.ds
dt= =
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188 Chapter 2 Differentiation
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17. [ ]
( )
2 2
3
22
1 1 9because 2 3
3 3 4
3
4
10
49
4 9
V r h h h r h
h
dV
dt
dV dtdV dh dhh
dt dt dt h
π π
π
ππ
= = =
=
=
= =
When 15,h =
( )( )2
4 10 8ft/min.
4059 15
dh
dt ππ= =
18. 2
23
2
2
150
1010
10 100
3
100100
3
V r h
dV
dth
h r r
hV h h
dV dhh
dt dtdh dV
dt h dt
π
ππ
π
π
=
=
= =
= =
=
=
When ( )
( )2
100 20035, 150 in. sec.
493 35
dhh
dt ππ= = =
19.
(a) Total volume of pool ( )( )( ) ( )( )( ) 312 12 6 1 6 12 144 m
2= + =
Volume of 1 m of water ( )( )( ) 311 6 6 18 m
2= = (see similar triangle diagram)
% pool filled ( )18100% 12.5%
144= =
(b) Because for 0 2, 6 ,h b h≤ ≤ = you have
( ) ( ) 216 3 3 6 18
2V bh bh h h h= = = =
( )
1 1 1 136 m/min.
4 144 144 1 144
dV dh dhh
dt dt dt h= = = = =
20. ( ) ( )2112 6 6 since
2V bh bh h b h= = = =
(a) 1
1212
dV dh dh dVh
dt dt dt h dt= =
When ( )( )1 1
1 and 2, 2 ft/min.12 1 6
dV dhh
dt dt= = = =
(b) If ( )( ) 33 1 1 3 in./min ft/min and 2 ft, then 12 2 ft /min.
8 32 32 4
dh dVh
dt dt = = = = =
h
r
1
1
3
6
12
2
h = 1
12
b = 6
3 ft
3 ft
h ft
12 ft
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Section 2.6 Related Rates 189
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21. 2 2 225
2 2 0
2because 2.
x y
dx dyx y
dt dtdy x dx x dx
dt y dt y dt
+ =
+ =
− −= ⋅ = =
(a) When ( )2 7 7
7, 576 24, ft/sec.24 12
dyx y
dt
−= = = = = −
When ( )2 15 3
15, 400 20, ft/sec.20 2
dyx y
dt
−= = = = = −
When ( )2 24 48
24, 7, ft/sec.7 7
dyx y
dt
−= = = = −
(b) 1
2
1
2
A xy
dA dy dxx y
dt dt dt
=
= +
From part (a) you have 7
7, 24, 2, and .12
dx dyx y
dt dt= = = = − So,
( ) 21 7 5277 24 2 ft /sec.
2 12 24
dA
dt
= − + =
(c)
22
22
tan
1sec
1cos
x
y
d dx x dy
dt y dt y dt
d dx x dy
dt y dt y dt
θ
θθ
θ θ
=
= ⋅ − ⋅
= ⋅ − ⋅
Using 7
7, 24, 2,12
dx dyx y
dt dt= = = = − and
24cos ,
25θ = you have
( )( )
2
2
24 1 7 7 12 rad/sec.
25 24 12 1224
d
dt
θ = − − =
22. 2 2 25
2 2 0
0.15because 0.15
+ =
+ =
= − ⋅ = − =
x y
dx dyx y
dt dtdx y dy y dy
dt x dt x dt
When 18.75
2.5, 18.75, 0.15 0.26 m/sec.2.5
dxx y
dt= = = − ≈ −
25y
x
25y
x
θ
y
x
5
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190 Chapter 2 Differentiation
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23. When 2 26, 12 6 6 3,y x= = − = and ( )22 12 108 36 12.s x y= + − = + =
( )
( )( )
( )
22 212
2 2 12 1 2
12
+ − =
+ − − =
+ − =
x y s
dx dy dsx y s
dt dt dtdx dy ds
x y sdt dt dt
Also, 2 2 212 .x y+ =
2 2 0dx dy dy x dx
x ydt dt dt y dt
−+ = =
So, ( )12 .dx x dx ds
x y sdt y dt dt
−+ − =
( )( )
( )( )( )12 612 1 30.2
12 155 312 6 3
dx x ds dx sy dsx x s
dt y dt dt x dt
− −− + = = ⋅ = − = =
m/sec (horizontal)
( )36 3 1
m/sec (vertical)6 15 5
dy x dx
dt y dt
−− −= = ⋅ =
24. Let L be the length of the rope.
(a) 2 2144
2 2
4since 4 ft/sec
L x
dL dxL x
dt dt
dx L dL L dL
dt x dt x dt
= +
=
= ⋅ = − = −
When 13:L =
( )2 144 169 144 5
4 13 5210.4 ft/sec
5 5
= − = − =
= − = − = −
x L
dx
dt
Speed of the boat increases as it approaches the dock.
12
( , )x y
s
x
12 − y
y
4 ft/sec
13 ft
12 ft
(b) If
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Section 2.6 Related Rates 191
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25. (a)
( ) ( )
2 2 2
450
600
2 2 2
s x y
dx
dtdy
dtds dx dy
s x ydt dt dt
x dx dt y dy dtds
dt s
= +
= −
= −
= +
+=
When 225x = and 300,y = 375s = and
( ) ( )225 450 300 600750 mi/h.
375
ds
dt
− + −= = −
(b) 375 1
h 30 min750 2
t = = =
26. 2 2 2
2 0 2 because 0
x y s
dx ds dyx s
dt dt dt
dx s ds
dt x dt
+ =
+ = =
=
When 10, 100 25 75 5 3,s x= = − = =
( )10 480240 160 3 277.13 mi/h.
5 3 3
dx
dt= = = ≈
27. 2 2 290
20
25
2 2
s x
x
dx
dtds dx ds x dx
s xdt dt dt s dt
= +=
= −
= = ⋅
When 2 220, 90 20 10 85,x s= = + =
( )20 5025 5.42 ft/sec.
10 85 85
ds
dt
−= − = ≈ −
28. 2 2 290
90 20 70
25
s x
x
dx
dtds x dx
dt s dt
= += − =
=
= ⋅
When 2 270, 90 70 10 130,x s= = + =
( )70 17525 15.35 ft/sec.
10 130 130
ds
dt= = ≈
29. (a)
( )
1515 15 6
6
5
3
5
5 5 255 ft/sec
3 3 3
yy x y
y x
y x
dx
dtdy dx
dt dt
= − =−
=
=
= ⋅ = =
(b) ( ) 25 10
5 ft/sec3 3
d y x dy dx
dt dt dt
−= − = − =
−100 100 200 300
100
200
300
y
x
sy
x
5 mi
x
s
y
x
s
x
90 ft
20 ft
Home
1st
2nd
3rd
s
x
90 ft
20 ft
Home
1st3rd
2nd
15
6
yx
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192 Chapter 2 Differentiation
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30. (a)
( )
20
6
20 20 6
14 20
10
7
5
10 10 505 ft/sec
7 7 7
y
y x
y x y
y x
y x
dx
dtdy dx
dt dt
=−
− ==
=
= −
−= = − =
31. ( ) 2 21sin , 1
2 6
tx t x y
π= + =
(a) Period: 2
12 seconds6
ππ
=
(b) When 2
21 1 3, 1 m.
2 2 2x y
= = − =
Lowest point: 3
0,2
(c) When 1
,4
x =
2
1 151 and 1:
4 4
1cos cos
2 6 6 12 6
y t
dx t t
dt
π π π π
= − = =
= =
2 2 1
2 2 0
x y
dx dy dy x dxx y
dt dt dt y dt
+ =−+ = =
So, 1 4
cos12 615 4
1 3 1 5.
12 2 24 12015 5
dy
dt
π π
π π π
= − ⋅
− − − = = =
Speed 5 5
m/sec120 120
π π−= =
32. ( ) 2 23sin , 1
5x t t x yπ= + =
(a) Period: 2
2 secondsπ
π=
(c) When 2
3 1 15, 1 and
10 4 4 = = − =
x y
3 3 1 1
sin sin10 5 2 6
π π= = =t t t
2 2
3cos
5
1
2 2 0
dxt
dt
x y
dx dy dy x dxx y
dt dt dt y dt
π π=
+ =−+ = =
So, 3 10 3
cos5 615 4
9 9 5.
12525 5
dy
dt
ππ
π π
− = ⋅
− −= =
Speed 9 5
0.5058 m/sec125
π−= ≈
33. Because the evaporation rate is proportional to the surface area, ( )24 .dV dt k rπ= However, because ( ) 34 3 ,V rπ= you
have 24 .dV dr
rdt dt
π= Therefore, ( )2 24 4 .dr dr
k r r kdt dt
π π= =
34. (i) (a) negative positivedx dy
dt dt
(b) positive negativedy dx
dt dt
(ii) (a) negative negativedx dy
dt dt
(b) positive positivedy dx
dt dt
20
6
yx
(b)
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Section 2.6 Related Rates 193
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35. (a) ( )3dy dt dx dt= means that y changes three times
as fast as x changes.
(b) y changes slowly when 0 or .x x L≈ ≈ y changes more rapidly when x is near the middle of the interval.
36. No. 3 2, 3dV ds
V s sdt dt
= =
If ds
dtis constant, then
dV
dtis 3s2 times that constant.
37. 1 2
1
2
1 22 2 2
1 2
1 1 1
1
1.5
1 1 1
R R R
dR
dtdR
dtdR dR dR
R dt R dt R dt
= +
=
=
⋅ = ⋅ + ⋅
When 1 50R = and 2 75:R =
30R =
( )( )
( )( )
( )2
2 2
1 130 1 1.5 0.6 ohm/sec
50 75
dR
dt
= + =
38.
1
V IR
dV dR dII R
dt dt dtdI dV I dR
dt R dt R dt
=
= +
= −
When 12, 4, 3,dV
V Rdt
= = = and
122, 3
4
dR VI
dt R= = = = and
( ) ( )1 3 33 2 amperes sec.
4 4 4
dI
dt= − = −
39. sin 18x
y° =
( )( )
2
10
sin 18 275 84.9797 mi/hr
x dy dx
y dt y dt
dx x dy
dt y dt
= − ⋅ + ⋅
= ⋅ = ° ≈
40.
2
2
tan50
4 m/sec
1sec
501
cos50
y
dy
dtd dy
dt dtd dy
dt dt
θ
θθ
θ θ
=
=
⋅ =
= ⋅
When 50, ,4
yπθ= = and
2cos .
2θ = So,
( )2
1 2 14 rad/sec.
50 2 25
d
dt
θ = =
41.
( )
( )
( )
2
2
2 2 2
10sin
1 ft/sec
10cos
10sec
10 251
25 25 10
10 1 2
25 5 21 25 21
2 210.017 rad/sec
525
xdx
dt
d dx
dt x dt
d dx
dt x dt
θ
θθ
θ θ
=
= −
− = ⋅
−=
−= −−
= =
= ≈
xy
18°
50
y
xθ
y
x
10
θ
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194 Chapter 2 Differentiation
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42.
( )
( ) ( )
22
22
2 2 2
2
2
2 2
tan , 5
600 mi/h
5sec
5 5cos
5 1
5
1sin 600 120 sin
5
yy
xdx
dtd dx
dt x dt
d dx x dx
dt x dt L x dt
dx
L dt
θ
θθ
θ θ
θ θ
= =
= −
= − ⋅
= − = −
= −
= − − =
(a) When 30 ,θ = °
120 1
30 rad/h rad/min.4 2
d
dt
θ = = =
(b) When 60 ,θ = °
3 3
120 90 rad/h rad/min.4 2
d
dt
θ = = =
(c) When 75 ,θ = °
2120 sin 75 111.96 rad/h 1.87 rad/min.d
dt
θ = ° ≈ ≈
43.
( )
2
2
tan50
30 2 60 rad/min rad/sec
1sec
50
50 sec
x
d
dt
d dx
dt dt
dx d
dt dt
θ
θ π π π
θθ
θθ
=
= = =
=
=
(a) When 200
30 , ft/sec.3
dx
dt
πθ = ° =
(b) When 60 , 200 ft/sec.dx
dtθ π= ° =
(c) When 70 , 427.43 ft/sec.dx
dtθ π= ° ≈
44. ( )( )10 rev/sec 2 rad/rev 20 rad/secd
dt
θ π π= =
(a)
( )
cos301
sin30
30 sin
30 sin 20
600 sin
x
d dx
dt dtdx d
dt dt
θ
θθ
θθ
θ ππ θ
=
− =
= −
= −= −
(b)
(c) 600 sin is greatest whendx dt π θ= −
( )sin 1 or 90 180 .2
n nπθ θ π= = + ° + ⋅ °
( )is least when or 180 .dx dt n nθ π= ⋅ °
(d) For 30 ,θ = °
( ) 1600 sin 30 600 300 cm/sec.
2
dx
dtπ π π= − ° = − = −
For 60 ,θ = °
( )600 sin 60
3600 300 3 cm/sec.
2
dx
dtπ
π π
= − °
= − = −
45. (a) ( )
2 2
1 2sin 2 sin
2 2
cos cos2 2
1 12 sin cos
2 2 2 2
2 sin cos sin2 2 2 2
bb s
sh
h ss
A bh s s
s s
θ θ
θ θ
θ θ
θ θ θ
= =
= =
= =
= =
(b) 2 1
cos where rad/min.2 2
dA s d d
dt dt dt
θ θθ= =
When 2 23 1 3
, .6 2 2 2 8
dA s s
dt
πθ = = =
When 2 21 1
, .3 2 2 2 8
dA s s
dt
πθ = = =
(c) If s andd
dt
θis constant,
dA
dtis proportional to cos .θ
xθ
y = 5L
x
50 ft
θ
Police
xθ
30
x
P
−2000
0
2000
4π
b
s s
h
θ
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Section 2.6 Related Rates 195
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46. tan 50 tan50
xxθ θ= =
2
2
2
50 sec
2 50 sec
1cos ,
25 4 4
dx d
dt dtd
dtd
dt
θθ
θθ
θ π πθ θ
=
=
= − ≤ ≤
47. (a) Using a graphing utility,
( ) 3 20.0096 0.559 10.54 61.5.r f f f f= − + −
(b) ( )20.0288 1.118 10.54dr dr df df
f fdt df dt dt
= = − +
For 9, 16.3t f= = from the table under the year
2009.
Also, 1.25,df
dt= so you have
( ) ( )( ) ( )20.0288 16.3 1.118 16.3 10.54 1.25
0.03941 million participants per year.
dr
dt= − +
= −
48. ( )
( )( )
24.9 20
9.8
1 4.9 20 15.1
1 9.8
y t t
dyt
dt
y
y
= − +
= −
= − + =
′ = −
By similar triangles: 20
1220 240
y
x xx xy
=−
− =
When 15.1:y = ( )( )
20 240 15.1
20 15.1 240
240
4.9
x x
x
x
− =
− =
=
20 240
20
20
x xy
dx dy dxx y
dt dt dtdx x dy
dt y dt
− =
= +
=−
At ( )240 4.91, 9.8 97.96 m/sec.
20 15.1
dxt
dt= = − ≈ −
−
49. 2 2 25;x y+ = acceleration of the top of the ladder 2
2
d y
dt=
First derivative: 2 2 0
0
dx dyx y
dt dtdx dy
x ydt dt
+ =
+ =
Second derivative: 2 2
2 2
2 22 2
2 2
0
1
d x dx dx d y dy dyx y
dt dt dt dt dt dt
d y d x dx dyx
dt y dt dt dt
+ ⋅ + + ⋅ =
= − − −
When 7
7, 24, ,12
dyx y
dt= = = − and 2
dx
dt= (see Exercise 25). Because
dx
dtis constant,
2
20.
d x
dt=
( ) ( )22
2 22
1 7 1 49 1 6257 0 2 4 0.1808 ft/sec
24 12 24 144 24 144
d y
dt
= − − − − = − − = − ≈ −
12
20y
(0, 0)x
x
y
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196 Chapter 2 Differentiation
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50. 2 2144 ;L x= + acceleration of the boat 2
2
d x
dt=
First derivative: 2 2dL dx
L xdt dtdL dx
L xdt dt
=
=
Second derivative: 2 2
2 2
2 22 2
2 2
1
d L dL dL d x dx dxL x
dt dt dt dt dt dt
d x d L dL dxL
dt x dt dt dt
+ ⋅ = + ⋅
= + −
When 13, 5, 10.4,dx
L xdt
= = = − and 4dL
dt= − (see Exercise 28). Because
dL
dtis constant,
2
20.
d L
dt=
( ) ( ) ( )
[ ] [ ]
22 2
2
2
113 0 4 10.4
5
1 116 108.16 92.16 18.432 ft/sec
5 5
d x
dt = + − − −
= − = − = −
Review Exercises for Chapter 2
1. ( )
( ) ( ) ( )0
0
0
12
lim
12 12lim
0lim 0
x
x
x
f x
f x x f xf x
x
x
x
Δ →
Δ →
Δ →
=
+ Δ −′ =
Δ−=
Δ
= =Δ
2. ( )
( ) ( ) ( )
( ) ( )0
0
0
0
5 4
lim
5 4 5 4lim
5 5 4 5 4lim
5lim 5
x
x
x
x
f x x
f x x f xf x
x
x x x
xx x x
xx
x
Δ →
Δ →
Δ →
Δ →
= −
+ Δ −′ =
Δ + Δ − − − =
Δ+ Δ − − +=
ΔΔ= =Δ
3. ( )
( ) ( ) ( )
( ) ( )
( ) ( ) ( ) ( )
( ) ( ) ( ) ( )
( ) ( )
3
0
3 3
0
2 33 2 3
0
2 32
0
22
0
2
2 1
lim
2 1 2 1lim
3 3 2 2 1 2 1lim
3 3 2lim
3 3 2lim
1
3 2
Δ →
Δ →
Δ →
Δ →
Δ →
= − +
+ Δ −′ =
Δ
+ Δ − + Δ + − − + =Δ
+ Δ + Δ + Δ − − Δ + − + −=
Δ
Δ + Δ + Δ − Δ=
Δ
+ Δ + Δ − =
= −
x
x
x
x
x
f x x x
f x x f xf x
x
x x x x x x
x
x x x x x x x x x x
x
x x x x x x
x
x x x x
x
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Review Exercises for Chapter 2 197
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4. ( )
( ) ( ) ( )
( )( ) ( ) ( )
0
20 0 0 0
6
lim
6 66 6 6 6 6 6
lim lim lim lim
x
x x x x
f xx
f x x f xf x
x
x x x xx x xx x x x x x x x x x x x x
Δ →
Δ → Δ → Δ → Δ →
=
+ Δ −′ =Δ
− − + Δ − Δ − −+ Δ= = = = =Δ Δ + Δ Δ + Δ + Δ
5. ( )
( ) ( ) ( )
( )
( )( )
( ) ( )
2
2
2
2
2
2
2 3 , 2
22 lim
2
2 3 2lim
2
2 2 1lim
2
lim 2 1 2 2 1 5
x
x
x
x
g x x x c
g x gg
x
x x
x
x x
x
x
→
→
→
→
= − =
−′ =
−− −
=−
− +=
−= + = + =
6. ( ) 1, 3
4f x c
x= =
+
( ) ( ) ( )
( )( )
( )
3
3
3
3
33 lim
3
1 1
4 7lim3
7 4lim
3 4 7
1 1lim
4 7 49
x
x
x
x
f x ff
x
xx
x
x x
x
→
→
→
→
−′ =
−
−+=
−− −=
− +
−= = −+
7. f is differentiable for all 3.x ≠
8. f is differentiable for all 1.x ≠ −
9. 25
0
y
y
=′ =
10. ( )
( )6
0
f t
f t
π=
′ =
11. ( )( )
3 2
2
11
3 22
f x x x
f x x x
= −
′ = −
12. ( )( )
5 4
4 3
3 2
' 15 8
g s s s
g s s s
= −
= −
13. ( )
( )
3 1 2 1 3
1 2 2 3
3 2
6 3 6 3
3 13
h x x x x x
h x x xx x
− −
= + = +
′ = + = +
14. ( )
( )
1 2 5 6
1 2 11 61 5
2 6
f x x x
f x x x
−
− −
= −
′ = +
15. ( )
( )
2
33
2
34 4
3 3
g t t
g t tt
−
−
=
−′ = = −
16. ( )
( )
44
55
8 8
5 532 32
5 5
h x xx
h x xx
−
−
= =
′ = − = −
17. ( )( )
4 5 sin
4 5 cos
f
f
θ θ θ
θ θ
= −
′ = −
18. ( )( )
4 cos 6
4 sin
g
g
α α
α α
= +
′ = −
19. ( )
( )
sin3 cos
4cos
3 sin4
f
f
θθ θ
θθ θ
= −
′ = − −
20. ( )
( )
5 sin2
35 cos
23
g
g
αα α
αα
= −
′ = −
21. ( ) ( )
( ) ( )
( )
33
44
4
2727 , 3, 1
8127 3
813 1
3
f x xx
f x xx
f
−
−
= =
′ = − = −
′ = − = −
22. ( ) ( )( )( )
23 4 , 1, 1
6 4
1 6 4 2
f x x x
f x x
f
= − −
′ = −
′ = − =
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198 Chapter 2 Differentiation
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23. ( ) ( )( )( )
5
4
4 3 sin , 0, 0
20 3 cos
0 3 1 2
f x x x x
f x x x
f
= + −
′ = + −
′ = − =
24. ( ) ( )( )( )
5 cos 9 , 0, 5
5 sin 9
0 5 sin 0 9 9
f x x x
f x x
f
= −
′ = − −
′ = − − = −
25.
( )
200
100
F T
F tT
=
′ =
(a) When ( )4, 4 50T F′= = vibrations/sec/lb.
(b) When ( ) 13
9, 9 33T F′= = vibrations/sec/lb.
26. 26
12
=
=
S x
dSx
dx
When ( ) 24, 12 4 48 in. in.dS
xdx
= = =
27. ( ) 20 0 0 016 ; 600, 30s t t v t s s v= − + + = = −
(a) ( )( ) ( )
216 30 600
32 30
s t t t
s t v t t
= − − +
′ = = − −
(b) ( ) ( )3 1
Average velocity3 1
366 554
294 ft/sec
s s−=
−−=
= −
(c) ( ) ( )( ) ( )1 32 1 30 62 ft/sec
3 32 3 30 126 ft/sec
v
v
= − − = −
= − − = −
(d) ( ) 20 16 30 600s t t t= = − − +
Using a graphing utility or the Quadratic Formula, 5.258t ≈ seconds.
(e) When
( ) ( )5.258, 32 5.258 30 198.3 ft/sec.t v t≈ ≈ − − ≈ −
28. ( )
( ) ( )( ) ( )( ) ( )
20 0
2
1
2
16 450
32
2 32 2 64 ft sec
5 32 5 160 ft sec
= − + +
= − +′= = −
= − = −
= − = −
s t gt v t s
t
v t s t t
v
v
29. ( ) ( )( )( ) ( )( ) ( )( )
( )
2 2
2 2
3 2 3 2
3 2
3 2
5 8 4 6
5 8 2 4 4 6 10
10 16 20 32 10 40 60
20 60 44 32
4 5 15 11 8
f x x x x
f x x x x x x
x x x x x x
x x x
x x x
= + − −
′ = + − + − −
= + − − + − −
= − − −
= − − −
30. ( ) ( )( )( ) ( )( ) ( )( )
3
3 2
3 3 2
3 2
2 5 3 4
2 5 3 3 4 6 5
6 15 18 24 15 20
24 24 30 20
g x x x x
g x x x x x
x x x x x
x x x
= + −
′ = + + − +
= + + − + −
= − + −
31. ( ) ( )( ) ( )
9 1 sin
9 1 cos 9 sin
9 cos cos 9 sin
f x x x
f x x x x
x x x x
= −
′ = − +
= − +
32. ( )( ) ( ) ( )
5
5 4
5 4
2 cos
2 sin cos 10
2 sin 10 cos
f t t t
f t t t t t
t t t t
=
′ = − +
= − +
33. ( )
( ) ( )( ) ( )( )( )
( )( )
2
2
2 2
22
2
22
1
1
1 2 1 1 2
1
1
1
x xf x
x
x x x x xf x
x
x
x
+ −=−
− + − + −′ =
−
− +=
−
34. ( )
( ) ( )( ) ( )( )( )
( )
( )( )( )
2
2
22
2 2
22
22
2 22 2
2 7
4
4 2 2 7 2
4
2 8 4 14
4
2 7 42 14 8
4 4
xf x
x
x x xf x
x
x x x
x
x xx x
x x
+=++ − +
′ =+
+ − −=+
− + −− − += =+ +
35.
( ) ( )
4
3 4
2
3 4
2
cos
cos 4 sin
cos
4 cos sin
cos
xy
x
x x x xy
x
x x x x
x
=
− −′ =
+=
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Review Exercises for Chapter 2 199
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36.
( ) ( )( )( )
4
4 3
2 54
sin
cos sin 4 cos 4 sin
xy
x
x x x x x x xy
xx
=
− −′ = =
37. 2
2
3 sec
3 sec tan 6 sec
y x x
y x x x x x
=
′ = +
38. 2
2 2
tan
sec 2 tan
y x x
y x x x x
= −
′ = − −
39. cos sin
sin cos cos sin
y x x x
y x x x x x x
= −′ = − + − = −
40. ( )( ) ( )
4
3 4 2
3 4 2
cot 3 cos
4 cot csc 3 cos 3 sin
4 cot csc 3 cos 3 sin
g x x x x x
g x x x x x x x x
x x x x x x x
= +
′ = + − + −
= − + −
41. ( ) ( )( ) ( )( ) ( )( ) ( )( )
( )
2
2
2 2 2
2 5 , 1, 6
2 2 5 1
2 4 5 3 4 5
1 3 4 5 4
f x x x
f x x x x
x x x x x
f
= + + −
′ = + + +
= + + + = + +′ − = − + =
Tangent line: ( )6 4 1
4 10
y x
y x
− = +
= +
42. ( ) ( )( ) ( )( ) ( )( ) ( )( )
2
2
2 2
2
4 6 1 , 0, 4
4 2 6 6 1 1
2 2 24 6 1
3 4 25
f x x x x
f x x x x x
x x x x
x x
= − + −
′ = − + + + −
= − − + + −
= + −
( )0 0 0 25 25f ′ = + − = −
Tangent line: ( )4 25 0
25 4
y x
y x
− = − −
= − +
43. ( )
( ) ( ) ( )( ) ( )
( )
2 2
1 1, , 3
1 2
1 1 2
1 1
1 28
2 1 4
xf x
x
x xf x
x x
f
+ = − − − − + −′ = =
− −
− ′ = = −
Tangent line: 1
3 82
8 1
y x
y x
+ = − −
= − +
44. ( )
( ) ( )( ) ( )( )( )
( )
2
2
cos, , 1
cos 2
cos sin cos sin
cos
2 sin
cos
22
2 1
xf x
x
x x x xf x
x
x
x
f
π
π
1 + = 1 −
1 − − − 1 +′ =
1 −
−=1 −
− ′ = = −
Tangent line: 1 22
2 1
y x
y x
π
π
− = − −
= − + +
45. ( )( )( )
3
2
8 5 12
24 5
48
g t t t
g t t
g t t
= − − +
′ = − −
′′ = −
46. ( )( )
( )
2 2
3
44
6 7
12 14
3636 14 14
h x x x
h x x x
h x xx
−
−
−
= +
′ = − +
′′ = + = +
47. ( )( )( )
5 2
3 2
1 2
752
225 2254 4
15f x x
f x x
f x x x
=
′ =
′′ = =
48. ( )( )
( )
5 1 5
4 5
9 59 5
20 20
4
16 16
5 5
f x x x
f x x
f x xx
−
−
= =
′ =
−′′ = = −
49. ( )( )( ) ( )
2
2
3 tan
3 sec
6 sec sec tan
6 sec tan
f
f
f
θ θ
θ θ
θ θ θ θ
θ θ
=
′ =
′′ =
=
50. ( )( )( )
10 cos 15 sin
10 sin 15 cos
10 cos 15 sin
h t t t
h t t t
h t t t
= −
′ = − −
′′ = − +
51. ( )( )( ) ( )
2
2
4 cot
4 csc
8 csc csc cot
8 csc cot
g x x
g x x
g x x x x
x x
=
′ = −
′′ = − −
=
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200 Chapter 2 Differentiation
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52. ( )( ) ( )( ) ( ) ( )
( )2
3 2
12 csc
12 csc cot 12 csc cot
12 csc csc 12 cot csc cot
12 csc csc cot
= −
′ = − − =
′′ = − + −
= − +
h t t
h t t t t t
h t t t t t t
t t t
53. ( )( ) ( )( )( ) ( )
2
2
2
20 , 0 6
2
3 20 3 11 m/sec
3 2 3 6 m/sec
= − ≤ ≤′= = −
= − =
= − = −
v t t t
a t v t t
v
a
54. ( )
( ) ( ) ( )( )
( ) ( )
2
2 2
90
4 104 10 90 90 4
4 10
900 225
4 10 2 5
=++ −
=+
= =+ +
tv t
tt t
a tt
t t
(a) ( )
( ) 2
901 6.43 ft/sec
14225
1 4.59 ft/sec49
v
a
= ≈
= ≈
(b) ( ) ( )
( ) 22
90 55 15 ft/sec
30225
5 1 ft/sec15
v
a
= =
= =
(c) ( ) ( )
( ) 22
90 1010 18 ft/sec
50225
10 0.36 ft/sec25
v
a
= =
= =
55. ( )( ) ( ) ( )
4
3 3
7 3
4 7 3 7 28 7 3
y x
y x x
= +
′ = + = +
56. ( )( ) ( ) ( )
32
2 22 2
6
3 6 2 6 6
y x
y x x x x
= −
′ = − = −
57. ( )
( )
( ) ( )
( )
3232
42
42
15
5
3 5 2
6
5
−
−
= = ++
′ = − +
= −+
y xx
y x x
x
x
58. ( )( )
( )
( ) ( ) ( )( )
2
2
3
3
15 1
5 1
102 5 1 5
5 1
−
−
= = ++
′ = − + = −+
f x xx
f x xx
59. ( )( )( ) ( )
5 cos 9 1
5 sin 9 1 9 45 sin 9 1
y x
y x x
= +
′ = − + = − +
60.
( )( )4
4 3 3 4
6 sin 3
6 cos 3 12 72 cos 3
y x
y x x x x
= −
′ = − = −
61.
( ) ( ) 2
sin 2
2 41 1 1
cos 2 2 1 cos 2 sin2 4 2
x xy
y x x x
= −
′ = − = − =
62.
( ) ( )( )
7 5
6 4
5 2
5 3
sec sec
7 5
sec sec tan sec sec tan
sec tan sec 1
sec tan
x xy
y x x x x x x
x x x
x x
= −
′ = −
= −
=
63. ( )( ) ( ) ( ) ( )( ) ( )
( ) ( )( ) ( )
5
4 5
4 5
4
4
6 1
5 6 1 6 6 1 1
30 6 1 6 1
6 1 30 6 1
6 1 36 1
y x x
y x x x
x x x
x x x
x x
= +
′ = + + +
= + + +
= + + +
= + +
64. ( ) ( ) ( )( ) ( ) ( ) ( )( )( ) ( )
( ) ( ) ( )( ) ( )
5 22 3
5 2 3 22 2 3 2
3 22 2 3
3 22 3
52
1 5
1 3 5 1 2
1 3 1 5 5
1 8 3 25
f s s s
f s s s s s s
s s s s s
s s s s
= − +
′ = − + + −
= − − + +
= − − +
65. ( )
( )( ) ( ) ( )( )
( )( )
( )( )
3
1 2 1 22
2
3 2
2
5 / 2
12
5
5 1 53
55
2 53
5 2 5
3 10
2 5
xf x
x
x x xxf x
xx
x xx
x x
x x
x
−
= +
+ − + ′ = ++
+ − =
+ +
+=
+
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66. ( )
( ) ( )( ) ( )( )( )
( )( )( )
2
2
2
22 2
2
32
5
3
3 1 5 252
3 3
2 5 10 3
3
xh x
x
x x xxh x
x x
x x x
x
+ = +
+ − ++ ′ = + +
+ − − +=
+
67. ( ) ( )
( ) ( ) ( )
( ) ( )
3
21 23 2
3
1 , 2, 3
1 31 3
2 2 1
122 2
2 3
f x x
xf x x x
x
f
−
= − −
−′ = − − =−
−′ − = = −
68. ( ) ( )
( ) ( ) ( )( )
( ) ( )( )
3 2
2 322 32
1, 3, 2
1 21 2
3 3 1
2 3 13
3 4 2
f x x
xf x x x
x
f
−
= −
′ = − =−
′ = =
69. ( )( )
( )
( )( ) ( ) ( )( )( ) ( )
( ) ( )
1 2
1 2 1 212
8, 0, 8
3 1
3 1 1 8 3 1 3
3 1
1 4 30 11
1
xf x
x
x x xf x
x
f
−
+=+
+ − + +′ =
+−′ = = −
70. ( )( )
( )
( ) ( ) ( ) ( )( )( ) ( )( )
( ) ( )( )
3
3 2
6
3 1, 1, 4
4 3
4 3 3 3 1 3 4 3 4
4 3
3 4 3 41 45
1
xf x
x
x x xf x
x
f
+=−
− − + −′ =
−
−′ = = −
71. 1 1
csc 2 , ,2 4 2
csc 2 cot 2
04
y x
y x x
y
π
π
=
′ = −
′ =
72.
2
csc 3 cot 3 , , 16
3 csc 3 cot 3 3 csc 3
0 3 36
y x x
y x x x
y
π
π
= +
′ = − −
′ = − = −
73. ( )( ) ( ) ( )
( )( )( ) ( )
3
2 2
8 5
3 8 5 8 24 8 5
24 2 8 5 8 384 8 5
y x
y x x
y x x
= +
′ = + = +
′′ = + = +
74. ( )
( )( ) ( ) ( )
( )( )( ) ( )( )
1
2 2
3
3
15 1
5 1
1 5 1 5 5 5 1
505 2 5 1 5
5 1
y xx
y x x
y xx
−
− −
−
= > ++
′ = − + = − +
′′ = − − + =+
75. ( )( )( ) ( )
2
2
cot
csc
2 csc csc cot
2 csc cot
f x x
f x x
f x x x x
x x
=
′ = −
′′ = − − ⋅
=
76.
( )
2
2
2 2
2 2
sin
sin 2 sin cos
2 sin cos 2 sin cos 2 cos 2 sin
4 sin cos 2 cos sin
y x x
y x x x x
y x x x x x x x x
x x x x x
=
′ = +
′′ = + + −
= + −
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202 Chapter 2 Differentiation
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77.
( )( )
( )
2
12
22
700
4 10
700 4 10
1400 2
4 10
Tt t
T t t
tT
t t
−
=+ +
= + +
− +′ =
+ +
(a)
( )( )2
When 1,
1400 1 218.667 deg/h.
1 4 10
t
T
=
− +′ = ≈ −
+ +
(b)
( )( )2
When 3,
1400 3 27.284 deg/h.
9 12 10
t
T
=
− +′ = ≈ −
+ +
(c)
( )( )2
When 5,
1400 5 23.240 deg/h.
25 20 10
t
T
=
− +′ = ≈ −
+ +
(d)
( )( )2
When 10,
1400 10 20.747 deg/h.
100 40 10
t
T
=
− +′ = ≈ −
+ +
78.
( ) ( )
( )
( )
( ) ( )
1 1cos 8 sin 8
4 41 1
sin 8 8 cos 8 84 4
2 sin 8 2 cos 8
At time ,4
1 1cos 8 sin 8
4 4 4 4 4
1 11 ft.
4 4
2 sin 8 2cos 84 4 4
2 0 2 1 2 ft/sec
y t t
y t t
t t
t
y
v t y
π
π π π
π π π
= −
′ = − −
= − −
=
= −
= =
′= = − − = − − = −
79. 2 2 64
2 2 0
2 2
x y
x yy
yy x
xy
y
+ =′+ =′ = −
′ = −
80.
( )
2 3
2
2
2
4 6
2 4 4 3 0
4 3 2 4
2 4
3 4
x xy y
x xy y y y
x y y x y
x yy
y x
+ − =
′ ′+ + − =
′− = − −
+′ =−
81.
( )
( )( )
3 3
3 2 2 3
3 2 3 2
3 2 3 2
3 2
3 2
2 2
2 2
4
3 3 0
3 3
3 3
3
3
3
3
x y xy
x y x y x y y y
x y xy y y x y
y x xy y x y
y x yy
x xy
y y xy
x x y
− =
′ ′+ − − =
′ ′− = −
′ − = −
−′ =−
−′ =
−
82.
( )( )
4
1 42 2
2 8
8 2
2
8
2 4
8 4
2 9
9 32
xy x y
yxy y
y x
xy y xy xy y
x xy y xy y
xy yy
x xy
x y y
x x y
x y
x y
= −
′ ′+ = −
′ ′+ = −
′+ = −
−′ =+
− −=
+ −
−=−
83.
( )( )
sin cos
cos sin sin cos
cos cos sin sin
sin sin
cos cos
x y y x
x y y y y x y x
y x y x y x y
y x yy
x x y
=′ ′+ = − +
′ − = − −
+′ =−
84. ( )( ) ( )
( ) ( )( )
( ) ( )
cos
1 sin 1
sin 1 sin
1 sincsc 1 1
sin
+ =
′− + + =
′− + = + +
+ +′ = − = − + −
+
x y x
y x y
y x y x y
x yy x
x y
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Review Exercises for Chapter 2 203
© 2018 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.
85.
( )( )
( )
2 2 10
2 2 0
At 3, 1 , 3
Tangent line: 1 3 3 3 10 0
1Normal line: 1 3 3 0
3
x y
x yy
xy
y
y
y x x y
y x x y
+ =′+ =
−′ =
′ = −
− = − − + − =
− = − − =
86.
( )
2 2 20
2 2 0
3At 6, 4 ,
2
− =′− =
′ =
′ =
x y
x yy
xy
y
y
Tangent line: ( )34 6
23
52
2 3 10 0
y x
y x
y x
− = −
= −
− + =
Normal line: ( )24 6
32
83
3 2 24 0
y x
y x
y x
− = − −
= − +
+ − =
87.
2 units/sec
12 4
2
=
=
= = =
y x
dy
dtdy dx dx dy
x xdt dt dt dtx
(a) 1
When , 2 2 units/sec.2
dxx
dt= =
(b) When 1, 4 units/sec.dx
xdt
= =
(c) When 4, 8 units/sec.dx
xdt
= =
88. 2Surface area 6 , lengthA x x= = = of edge
8dx
dt=
( )( ) 212 12 6.5 8 624 cm /secdA dx
xdt dt
= = =
89.
( )
( )( ) ( )
2
2 2
tan
3 2 rad/min
sec
tan 1 6 6 1
x
d
dt
d dx
dt dt
dxx
dt
θθ π
θθ
θ π π
=
=
=
= + = +
1
When ,2
1 156 1 km/min 450 km/h.
4 2
x
dx
dt
ππ π
=
= + = =
−4
−6 6
4
(3, 1)
−1
7
−1
11
(6, 4)
x
1θ
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204 Chapter 2 Differentiation
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90. ( )( )
( )( )
( ) ( )
( )
2
2
2
60 4.9
9.8
35 60 4.9
4.9 25
5
4.9
1tan 30
3
3
53 3 9.8 38.34 m/sec
4.9
s t t
s t t
s t
t
t
s t
x t
x t s t
dx ds
dt dt
= −
′ = −
= = −
=
=
= =
=
= = − ≈ −
Problem Solving for Chapter 2
1. (a) ( )22 2
2
, Circle
, Parabola
x y r r
x y
+ − =
=
Substituting:
( )
( )
2 2
2 2 2
2
2
2 0
2 1 0
y r r y
y ry r r y
y ry y
y y r
− = −
− + = −
− + =
− + =
Because you want only one solution, let 1
1 2 0 .2
r r− = = Graph 2y x= and 2
2 1 1.
2 4x y
+ − =
(b) Let ( ),x y be a point of tangency:
( ) ( )22 1 2 2 0 ,x
x y b x y b y yb y
′ ′+ − = + − = =−
Circle
2 2 ,y x y x′= = Parabola
Equating:
( )
2
2 1
1 1
2 2
xx
b y
b y
b y b y
=−
− =
− = = +
Also, ( )22 1x y b+ − = and 2y x= imply:
( )2
2 1 1 3 51 1 1 and
2 4 4 4y y b y y y y y b
+ − = + − + = + = = =
Center: 5
0,4
Graph 2y x= and 2
2 51.
4x y
+ − =
x t( )
s t( )
30°
3
−1
−3
3
3
−1
−3
3
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Problem Solving for Chapter 2 205
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2. Let ( )2,a a and ( )2, 2 5b b b− + − be the points of tangency. For 2, 2y x y x′= = and for 2 2 5,y x x= − + −
2 2.y x′ = − + So, 2 2 2 1,a b a b= − + + = or 1 .a b= − Furthermore, the slope of the common tangent line is
( ) ( )( )
( )( )
22 2 2
2 2
2 2
2
2
2 5 1 2 52 2
1
1 2 2 52 2
1 2
2 4 6 4 6 2
2 2 4 0
2 0
2 1 0
2, 1
a b b b b bb
a b b b
b b b bb
b
b b b b
b b
b b
b b
b
− − + − − + − += = − +
− − −
− + + − + = − +
− − + = − + − − = − − = − + == −
For 2, 1 1b a b= = − = − and the points of tangency are ( )1, 1− and ( )2, 5 .− The tangent line has slope
( )2: 1 2 1 2 1y x y x− − = − = = − −
For 1, 1 2b a b= − = − = and the points of tangency are ( )2, 4 and ( )1, 8 .− − The tangent line has slope
( )4: 4 4 2 4 4y x y x− = − = −
3. Let ( )( )
3 2
23 2 .
p x Ax Bx Cx D
p x Ax Bx C
= + + +
′ = + +
( )At 1, 1 : ( )At 1, 3 :− −
= 1 Equation 1
3 2 = 14 Equation 2
A B C D
A B C
+ + ++ +
= 3 Equation 3
3 2 = 2 Equation 4
A B C D
A B C
+ − + −+ + −
Adding Equations 1 and 3: 2 2 2B D+ = −
Subtracting Equations 1 and 3: 2 2 4A C+ = ( )12
2 2 5.D B= − − = −
Adding Equations 2 and 4: 6 2 12A C+ =
Subtracting Equations 2 and 4: 4 16B =
So, 4B = and ( )12
2 2 5.D B= − − = − Subtracting 2 2 4A C+ = and 6 2 12,A C+ =
you obtain 4 8 2.A A= = Finally, ( )12
4 2 0.C A= − = So, ( ) 3 22 4 5.p x x x= + −
y
x−8 −6
−6
−4
−4
4
6
8
10
−2 2 4 6 8 10
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206 Chapter 2 Differentiation
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4. ( ) cosf x a b cx= +
( ) sinf x bc cx′ = −
( )At 0, 1 : 1 Equation 1
3 3At , : cos Equation 2
4 2 4 2
sin 1 Equation 34
a b
ca b
cbc
π π
π
+ =
+ =
− =
From Equation 1, 1 .a b= − Equation 2 becomes
( ) 3 11 cos cos .
4 2 4 2
c cb b b b
π π − + = − + =
From Equation 3, ( )1
. So:sin 4
bc cπ
−=
( ) ( )1 1 1
cossin 4 sin 4 4 2
11 cos sin
4 2 4
c
c c c c
c cc
ππ π
π π
− + =
− =
Graphing the equation
( ) 1sin cos 1,
2 4 4
c cg c c
π π = + −
you see that many values of c will work. One answer:
( )1 3 3 12, , cos 2
2 2 2 2c b a f x x= = − = = −
5. (a) ( )( )
2, 2 , Slope 4 at 2, 4
Tangent line: 4 4 2
4 4
y x y x
y x
y x
′= = =
− = −
= −
(b) Slope of normal line: 1
4−
Normal line: ( )
( )( )
2
2
14 2
41 9
4 21 9
4 2
4 18 0
4 9 2 0
y x
y x
y x x
x x
x x
− = − −
= − +
= − + =
+ − =
+ − =
9
2,4
x = −
Second intersection point: 9 81
,4 16
−
(c) Tangent line: 0y =
Normal line: 0x =
6. (a) ( ) ( )( ) ( )( ) ( )( )
1 0 1
1 0 0
1 1 1
1
cos
0 1 0 1
0 0 0 0
1
f x x P x a a x
f P a a
f P a a
P x
= = +
= = =′ ′= = =
=
(c)
( )2P x is a good approximation of ( ) cosf x x= when x is near 0.
(d) Let be a point on the parabola
Tangent line at is
Normal line at is
To find points of intersection, solve:
The normal line intersects a second time at
x −1.0 −0.1 −0.001 0 0.001 0.1 1.0
0.5403 0.9950 1 0.9950 0.5403
0.5 0.9950 1 0.9950 0.5
(b)
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Problem Solving for Chapter 2 207
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(d) ( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )
( )
2 33 0 1 2 3
3 0 0
3 1 1
3 2 2
3 3 3
33
16
16
sin
0 0 0 0
0 1 0 1
0 0 0 2 0
0 1 0 6
= = + + +
= = =
′ ′= = =
′′ ′′= = =
′′′ ′′′= − = = −
= −
f x x P x a a x a x a x
f P a a
f P a a
f P a a
f P a a
P x x x
7. (a) 4 2 2 2 2
2 2 2 2 4
2 2 4
x a x a y
a y a x x
a x xy
a
= −
= −
± −=
2 2 4
1Graph:a x x
ya
−=
and 2 2 4
2 .a x x
ya
−= −
(b)
( ), 0a± are the x-intercepts,
along with ( )0, 0 .
8. (a) ( )( )
2 2 3
32
2
; , 0= − >
−=
b y x a x a b
x a xy
b
( )3
1Graphx a x
yb
−= and
( )3
2 .x a x
yb
−= −
(b) a determines the x-intercept on the right: ( ), 0 .a b affects the height.
(c) Differentiating implicitly:
( )( )
2 2 3 2 3
2 3
2
2 3
3 32 2
4 22
2
2 3 3 4
3 40
2
3 4
3 4
3
4
3 3 27 1
4 4 64 4
27 3 3
256 16
′ = − − = −
−′ = =
==
=
= − =
= = ±
b yy x a x x ax x
ax xy
b y
ax x
a x
ax
a a ab y a a
a ay y
b b
Two points: 2 23 3 3 3 3 3
, , ,4 16 4 16
a a a a
b b
−
3
−2
−3
2
a = 1a = 2
a = 12
(c) Differentiating implicitly:
Four points:
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208 Chapter 2 Differentiation
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9. (a) Line determined by ( )0, 30 and ( )90, 6 :
( )30 6 24 4 430 0 30
0 90 90 15 15y x x x y x
−− = − = − = − = − +−
When 100:x = ( )4 10100 30 3
15 3y = − + = >
As you can see from the figure, the shadow determined by the man extends beyond the shadow determined by the child.
(b) Line determined by ( )0, 30 and ( )60, 6 :
( )30 6 2 230 0 30
0 60 5 5y x x y x
−− = − = − = − +−
When 70:x = ( )270 30 2 3
5y = − + = <
As you can see from the figure, the shadow determined by the child extends beyond the shadow determined by the man.
(c) Need ( ) ( ) ( )0, 30 , , 6 , 10, 3d d + collinear.
( )30 6 6 3 24 3
80 feet0 10 10
dd d d d
− −= = =− − +
(d) Let y be the distance from the base of the street light to the tip of the shadow. You know that / 5.dx dt = −
For 80,x > the shadow is determined by the man.
5
30 6 4
y y xy x
−= = and 5 25
4 4
dy dx
dt dt
−= =
For 80,x < the shadow is determined by the child.
10 10 100
30 3 9 9
y y xy x
− −= = + and 10 50
9 9
dy dx
dt dt= = −
Therefore:
25, 80
450
, 0 809
xdy
dtx
− >= − < <
/dy dt is not continuous at 80.x =
ALTERNATE SOLUTION for parts (a) and (b):
(a) As before, the line determined by the man’s shadow is
4
3015
my x= − +
The line determined by the child’s shadow is obtained by finding the line through ( )0, 30 and ( )100, 3 :
( )30 3 2730 0 30
0 100 100cy x y x
−− = − = − +−
By setting 0,m cy y= = you can determine how far the shadows extend:
4 1Man: 0 30 112.5 112
15 227 1
Child: 0 30 111.11 111100 9
m
c
y x x
y x x
= = = =
= = = =
The man’s shadow is 1 1 7
112 111 12 9 18
− = ft beyond the child’s shadow.
30
90 100
(0, 30)
(90, 6)
y
x
(100, 3)
Not drawn to scale
30
60 70
(0, 30)
(60, 6)
y
x
(70, 3)
Not drawn to scale
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Problem Solving for Chapter 2 209
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(b) As before, the line determined by the man’s shadow is
2
305
my x= − +
For the child’s shadow,
( )30 3 2730 0 30
0 70 70cy x y x
−− = − = − +−
2Man: 0 30 75
527 700 7
Child: 0 30 7770 9 9
m
c
y x x
y x x
= = =
= = = =
So the child’s shadow is 7 7
77 75 29 9
− = ft beyond the man’s shadow.
10. (a)
( )
1 3 2 3
2 3
1
31
1 83
12 cm/sec
dy dxy x x
dt dtdx
dtdx
dt
−
−
= =
=
=
(b) ( ) ( ) ( )
( ) ( )
2 2 2 2
2 2
/ /12 2
2
8 12 2 1 98 49cm/sec
64 4 68 17
x dx dt y dy dtdD dx dyD x y x y x y
dt dt dt x y
+ = + = + + = +
+= = =
+
(c) ( ) ( )2
2
/ /tan sec
x dy dt y dx dty d
x dt x
θθ θ−
= ⋅ =
From the triangle, sec 68 8.θ = So ( ) ( )
( )8 1 2 12 16 4
rad/sec.64 68 64 68 17
d
dt
θ − −= = = −
11. (a) ( )( ) 2
275
275
27 ft/sec
ft/sec
v t t
a t
= − +
= −
(b) ( )
( ) ( ) ( )2
27 275 5
2710
27 0 27 5 seconds
5 5 27 5 6 73.5 feet
= − + = = =
= − + + =
v t t t t
s
(c) The acceleration due to gravity on Earth is greater in magnitude than that on the moon.
12. ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )0 0 0 0
1 1lim lim lim limx x x x
E x x E x E x E x E x E x E xE x E x E x
x x x xΔ → Δ → Δ → Δ →
+ Δ − Δ − Δ − Δ −′ = = = = Δ Δ Δ Δ
But, ( ) ( ) ( ) ( )0 0
0 10 lim lim 1.
x x
E x E E xE
x xΔ → Δ →
Δ − Δ −′ = = =
Δ Δ So, ( ) ( ) ( ) ( )0E x E x E E x′ ′= = exists for all x.
For example: ( ) .xE x e=
θ8
268
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210 Chapter 2 Differentiation
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13. ( ) ( ) ( ) ( ) ( ) ( ) ( )0 0 0
lim lim limx x x
L x x L x L x L x L x L xL x
x x xΔ → Δ → Δ →
+ Δ − + Δ − Δ′ = = =Δ Δ Δ
Also, ( ) ( ) ( )0
00 lim .
x
L x LL
xΔ →
Δ −′ =
Δ But, ( )0 0L = because ( ) ( ) ( ) ( ) ( )0 0 0 0 0 0 0.L L L L L= + = + =
So, ( ) ( )0L x L′ ′= for all x. The graph of L is a line through the origin of slope ( )0 .L′
14. (a)
(b) 0
0
sinlim 0.0174533
sinIn fact, lim .
180
z
z
z
zz
z
π→
→
≈
=
(c) ( ) ( )
( )( ) ( )
0
0
0 0
sin sinsin lim
sin cos sin cos sinlim
cos 1 sinlim sin lim cos
sin 0 cos cos180 180
z
z
z z
z z zdz
dz zz z z z z
z
z zz z
z z
z z zπ π
Δ →
Δ →
Δ → Δ →
+ Δ −=
Δ⋅ Δ + Δ ⋅ −=
Δ Δ − Δ = + Δ Δ
= + =
(d) ( )
( )
( ) ( ) ( ) ( )
90 sin 90 sin 1180 2
180 cos 180 1180
sin cos180
S
C
d dS z cz c cz C z
dz dz
π π
π
π
= = =
= = −
= = ⋅ =
(e) The formulas for the derivatives are more complicated in degrees.
15. ( ) ( )j t a t′=
(a) ( )j t is the rate of change of acceleration.
(b) ( )( )( )( ) ( )
28.25 66
16.5 66
16.5
0
s t t t
v t t
a t
a t j t
= − +
= − +
= −
′ = =
The acceleration is constant, so ( ) 0.j t =
(c) a is position.
b is acceleration.
c is jerk.
d is velocity.
z (degrees) 0.1 0.01 0.0001
0.0174524 0.0174533 0.0174533
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Chapter 2 DifferentiationChapter CommentsThe material presented in Chapter 2 forms the basis for the remainder of calculus. Much of it needs to be memorized, beginning with the definition of a derivative of a function found on page 103. Students need to have a thorough understanding of the tangent line problem and they need to be able to find an equation of a tangent line. Frequently, students will use the function f ′(x) as the slope of the tangent line. They need to understand that f ′(x) is the formula for the slope and the actual value of the slope can be found by substituting into f ′(x) the appropriate value for x. On pages 105–106 of Section 2.1, you will find a discussion of situations where the derivative fails to exist. These examples (or similar ones) should be discussed in class.
As you teach this chapter, vary your notations for the derivative. One time write y′; another time write dy�dx or f′(x). Terminology is also important. Instead of saying “find the derivative,” sometimes say, “differentiate.” This would be an appropriate time, also, to talk a little about Leibnitz and Newton and the discovery of calculus.
Sections 2.2, 2.3, and 2.4 present a number of rules for differentiation. Have your students memorize the Product Rule and the Quotient Rule (Theorems 2.7 and 2.8) in words rather than symbols. Students tend to be lazy when it comes to trigonometry and therefore, you need to impress upon them that the formulas for the derivatives of the six trigonometric functions need to be memorized also. You will probably not have enough time in class to prove every one of these differentiation rules, so choose several to do in class and perhaps assign a few of the other proofs as homework.
The Chain Rule, in Section 2.4, will require two days of your class time. Students need a lot of practice with this and the algebra involved in these problems. Many students can find the derivative of f(x) = x2√1 − x2 without much trouble, but simplifying the answer is often difficult for them. Insist that they learn to factor and write the answer without negative exponents. Strive to get the answer in the form given in the back of the book. This will help them later on when the derivative is set equal to zero.
Implicit differentiation is often difficult for students. Have students think of y as a function of x and therefore y3 is [ f(x)]3. This way they can relate implicit differentiation to the Chain Rule studied in the previous section.
Try to get your students to see that related rates, discussed in Section 2.6, are another use of the Chain Rule.
Section 2.1 The Derivative and the Tangent Line Problem
Section Comments2.1 The Derivative and the Tangent Line Problem—Find the slope of the tangent line to a
curve at a point. Use the limit definition to find the derivative of a function. Understand the relationship between differentiability and continuity.
Teaching Tips
Ask students what they think “the line tangent to a curve” means. Draw a curve with tangent lines to show a visual picture of tangent lines. For example:
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y = f(x)
x
y
x
y
y = f(x)
When talking about the tangent line problem, use the suggested example of finding the equation of the tangent line to the parabola y = x2 at the point (1, 1).
Compute an approximation of the slope m by choosing a nearby point Q(x, x2) on the parabola and computing the slope mPQ of the secant line PQ.
After going over Examples 1–3, return to Example 2 where f(x) = x2 + 1 and note that f′(x) = 2x. How can we find the equation of the line tangent to f and parallel to 4x − y = 0? Because the slope of the line is 4,
2x = 4
x = 2.
So, at the point (2, 5), the tangent line is parallel to 4x − y = 0. The equation of the tangent line is y − 5 = 4(x − 2) or y = 4x − 3.
Be sure to find the derivatives of various types of functions to show students the different types of techniques for finding derivatives. Some suggested problems are f(x) = 4x3 − 3x2, g(x) = 2�(x − 1), and h(x) = √2x + 5.
How Do You See It? Exercise
Page 108, Exercise 64 The figure shows the graph of g′.
x
g ′
−4−6
−4
−6
6
6
4
4
2
y
(a) g′(0) =
(b) g′(3) =
(c) What can you conclude about the graph of g knowing that g′(1) = −83?
(d) What can you conclude about the graph of g knowing that g′(−4) = 73?
(e) Is g(6) − g(4) positive or negative? Explain.
(f) Is it possible to find g(2) from the graph? Explain.
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Solution
(a) g′(0) = −3
(b) g′(3) = 0
(c) Because g′(1) = −83, g is decreasing (falling) at x = 1.
(d) Because g′(−4) = 73, g is increasing (rising) at x = −4.
(e) Because g′(4) and g′(6) are both positive, g(6) is greater than g(4) and g(6) − g(4) > 0.
(f) No, it is not possible. All you can say is that g is decreasing (falling) at x = 2.
Suggested Homework Assignment
Pages 107–109: 1, 3, 7, 11, 21–27 odd, 37, 43–47 odd, 53, 57, 61, 77, 87, 93, and 95.
Section 2.2 Basic Differentiation Rules and Rates of Change
Section Comments2.2 Basic Differentiation Rules and Rates of Change—Find the derivative of a function
using the Constant Rule. Find the derivative of a function using the Power Rule. Find the derivative of a function using the Constant Multiple Rule. Find the derivative of a function using the Sum and Difference Rules. Find the derivatives of the sine function and of the cosine function. Use derivatives to find rates of change.
Teaching Tips
Start by showing proofs of the Constant Rule and the Power Rule. Students who are mathematics majors need to start seeing proofs early on in their college careers as they will be taking Functions of a Real Variable at some point.
Go over an example in class like f(x) = 5x2 + xx
. Show students that before differentiating
they can rewrite the function as f(x) = 5x + 1. Then they can differentiate to obtain f ′(x) = 5. Use this example to emphasize the prudence of examining the function first before differentiating. Rewriting the function in a simpler, equivalent form can expedite the differentiating process.
Give mixed examples of finding derivatives. Some suggested examples are:
f(x) = 3x6 − x2�3 + 3 sin x and g(x) = 43√x
+2
(3x)2 − 3 cos x + 7x + π3.
This will test students’ understanding of the various differentiation rules of this section.
How Do You See It? Exercise
Page 119, Exercise 76 Use the graph of f to answer each question. To print an enlarged copy of the graph, go to MathGraphs.com.
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x
f
CA
B
ED
y
(a) Between which two consecutive points is the average rate of change of the function greatest?
(b) Is the average rate of change of the function between A and B greater than or less than the instantaneous rate of change at B?
(c) Sketch a tangent line to the graph between C and D such that the slope of the tangent line is the same as the average rate of change of the function between C and D.
Solution
(a) The slope appears to be steepest between A and B.
(b) The average rate of change between A and B is greater than the instantaneous rate of change at B.
(c)
x
f
CA
B
ED
y
Suggested Homework Assignment
Pages 118–120: 1, 3, 5, 7–29 odd, 35, 39–53 odd, 55, 59, 65, 75, 85–89 odd, 91, 95, and 97.
Section 2.3 Product and Quotient Rules and Higher-Order Derivatives
Section Comments2.3 Product and Quotient Rules and Higher-Order Derivatives—Find the derivative of
a function using the Product Rule. Find the derivative of a function using the Quotient Rule. Find the derivative of a trigonometric function. Find a higher-order derivative of a function.
Teaching Tips
Some students have difficulty simplifying polynomial and rational expressions. Students should review these concepts by studying Appendices A.2–A.4 and A.7 in Precalculus, 10th edition, by Larson.
When teaching the Product and Quotient Rules, give proofs of each rule so that students can see where the rules come from. This will provide mathematics majors a tool for writing proofs, as each proof requires subtracting and adding the same quantity to achieve the desired results. For the Project Rule, emphasize that there are many ways to write the solution. Remind students that there must be one derivative in each term of the solution. Also, the Product Rule can be extended to more that just the product of two functions. Simplification is up to the discretion of the instructor. Examples such as f(x) = (2x2 − 3x)(5x3 + 6) can be done with or without the Product Rule. Show the class both ways.
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After the Quotient Rule has been proved to the class, give students the memorization tool of LO d HI – HI d LO. This will give students a way to memorize what goes in the numerator of the Quotient Rule.
Some examples to use are f(x) = 2x − 1x2 + 7x
and g(x) = 4 − (1�x)3 − x2 . Save f(x) for the next section
as this will be a good example for the Chain Rule. g(x) is a good example for first finding the least common denominator.
How Do You See It? Exercise
Page 132, Exercise 120 The figure shows the graphs of the position, velocity, and acceleration functions of a particle.
y
t1−1 4 5 6 7
84
1216
(a) Copy the graphs of the functions shown. Identify each graph. Explain your reasoning. To print an enlarged copy of the graph, go to MathGraphs.com.
(b) On your sketch, identify when the particle speeds up and when it slows down. Explain your reasoning.
Solution
(a) y
t1−1 4 5 6 7
8
4
12
16
s
v
a
s position function
v velocity function
a acceleration function
(b) The speed of the particle is the absolute value of its velocity. So, the particle’s speed is slowing down on the intervals (0, 4�3), and (8�3, 4) and it speeds up on the intervals (4�3, 8�3) and (4, 6).
1 3 5 6 7−4
−8
−12
−16
4
8
12
16
t
t =t = 44
3
t = 83 v
speed
Suggested Homework Assignment
Pages 129–132: 1, 3, 9, 13, 19, 23, 29–55 odd, 59, 61, 63, 75, 77, 91–107 odd, 111, 113, 117, and 131–135 odd.
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Section 2.4 The Chain Rule
Section Comments2.4 The Chain Rule—Find the derivative of a composite function using the Chain Rule.
Find the derivative of a function using the General Power Rule. Simplify the derivative of a function using algebra. Find the derivative of a trigonometric function using the Chain Rule.
Teaching Tips
Begin this section by asking students to consider finding the derivative of F(x) = √x2 + 1. F is a composite function. Letting y = f(u) = √u and u = g(x) = x2 + 1, then y = F(x) = f(g(x)) or F = f ∘ g. When stating the Chain Rule, be sure to state it using function notation and using Leibniz notation as students will see both forms when studying other courses with other texts. Following the definition, be sure to prove the Chain Rule as done on page 134.
Be sure to give examples that involve all rules discussed so far. Some examples include:
f(x) = (sin(6x))4, g(x) = (3 + sin(2x)3√x + 3 )
2
, and h(x) = (√x −2x ) ∙ [8x + cos(x2 + 1)]3.
You can use Exercise 98 on page 141 to review the following concepts:
• ProductRule
• ChainRule
• QuotientRule
• GeneralPowerRule
Students need to understand these rules because they are the foundation of the study of differentiation.
Use the solution to show students how to solve each problem. As you apply each rule, give the definition of the rule verbally. Note that part (b) is not possible because we are not given g′(3).
Solution
(a) f(x) = g(x)h(x)
f′(x) = g(x)h′(x) + g′(x)h(x)
f′(5) = (−3)(−2) + (6)(3) = 24
(b) f(x) = g(h(x))
f′(x) = g′(h(x))h′(x)
f′(5) = g′(3)(−2) = −2g′(3)
Not possible. You need g′(3) to find f′(5).
(c) f(x) = g(x)h(x)
f ′(x) = h(x)g′(x) − g(x)h′(x)[h(x)]2
f ′(x) = (3)(6) − (−3)(−2)(3)2 =
129
=43
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(d)
f
(x) = [g(x)]3
f′
(x) = 3[g(x)]2g′(x)
f′
(5) = 3(−3)2(6) = 162
How Do You See It? Exercise
Page 142, Exercise 106 The cost C (in dollars) of producing x units of a product is C = 60x + 1350. For one week, management determined that the number of units produced x at the end of t hours can be modeled by x = −1.6t3 + 19t2 − 0.5t − 1. The graph shows the cost C in terms of the time t.
1 2 3 4 5
Time (in hours)
Cost of Producing a Product
Cos
t (in
dol
lars
)
6 7 8
5,000
10,000
15,000
20,000
25,000
C
t
(a) Using the graph, which is greater, the rate of change of the cost after 1 hour or the rate of change of the cost after 4 hours?
(b) Explain why the cost function is not increasing at a constant rate during the eight-hour shift.
Solution
(a) According to the graph, C′(4) > C′(1).
(b) Answers will vary.
Suggested Homework Assignment
Pages 140–143: 1–53 odd, 63, 67, 75, 81, 83, 91, 97, 121, and 123.
Section 2.5 Implicit Differentiation
Section Comments2.5 Implicit Differentiation—Distinguish between functions written in implicit form and
explicit form. Use implicit differentiation to find the derivative of a function.
Teaching Tips
Material learned in this section will be vital for students to have for related rates. Be sure to ask
students to find dydx
when x = c.
You can use the exercise below to review the following concepts:
• Findingderivativeswhenthevariablesagreeandwhentheydisagree
• Usingimplicitdifferentiationtofindthederivativeofafunction
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Determine if the statement is true. If it is false, explain why and correct it. For each statement, assume y is a function of x.
(a) ddx
cos(x2) = −2x sin(x2)
(b) ddy
cos(y2) = 2y sin(y2)
(c) ddx
cos(y2) = −2y sin(y2)
Implicit differentiation is often difficult for students, so as you review this concept remind students to think of y as a function of x. Part (a) is true, and part (b) can be corrected as shown below. Part
(c) requires implicit differentiation. Note that the result can also be written as −2y sin(y2) dydx
.
Solution
(a) True
(b) False. ddy
cos(y2) = −2y sin(y2).
(c) False. ddx
cos(y2) = −2yy′ sin(y2).
A good way to teach students how to understand the differentiation of a mix of variables in part (c) is to let g = y. Then g′ = y′. So,
ddx
cos(y2) = ddx
cos(g2)
= −sin (g2) ∙ 2gg′
= −sin(y2) ∙ 2yy′
How Do You See It? Exercise
Page 151, Exercise 70 Use the graph to answer the questions.
x
y
−2 2
2
4
y3 − 9y2 + 27y + 5x2 = 47
(a) Which is greater, the slope of the tangent line at x = −3 or the slope of the tangent line at x = −1?
(b) Estimate the point(s) where the graph has a vertical tangent line.
(c) Estimate the point(s) where the graph has a horizontal tangent line.
Solution
(a) The slope is greater at x = −3.
(b) The graph has vertical tangent lines at about (−2, 3) and (2, 3).
(c) The graph has a horizontal tangent line at about (0, 6).
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Suggested Homework Assignment
Pages 149–150: 1–17 odd, 25–35 odd, 53, and 61.
Section 2.6 Related Rates
Section Comments2.6 Related Rates—Find a related rate. Use related rates to solve real-life problems.
Teaching Tips
Begin this lesson with a quick review of implicit differentiation with an implicit function in terms of x and y differentiated with respect to time. Follow this with an example similar to Example 1 on page 152, outlining the step-by-step procedure at the top of page 153 along with the guidelines at the bottom of page 153. Be sure to tell students, that for every related rate problem, to write down the given information, the equation needed, and the unknown quantity. A suggested problem to work out with the students is as follows:
A ladder 10 feet long rests against a vertical wall. If the bottom of the ladder slides away from the wall at a rate of 1 foot per second, how fast is the top of the ladder sliding down the wall when the bottom of the ladder is 6 feet from the wall?
Be sure to go over a related rate problem similar to Example 5 on page 155 so that students are exposed to working with related rate problems involving trigonometric functions.
How Do You See It? Exercise
Page 159, Exercise 34 Using the graph of f, (a) determine whether dy�dt is positive or negative given that dx�dt is negative, and (b) determine whether dx�dt is positive or negative given that dy�dt is positive. Explain.
(i)
x1 2 3 4
4
2
1 f
y (ii)
x−3 −2 −1 1 2 3
65432
f
y
Solution
(i) (a) dxdt
negative ⇒ dydt
positive
(b) dydt
positive ⇒ dxdt
negative
(ii) (a) dxdt
negative ⇒ dydt
negative
(b) dydt
positive ⇒ dxdt
positive
Suggested Homework Assignment
Pages 157–160: 1, 7, 11, 13, 15, 17, 21, 25, 29, and 41.
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Chapter 2 Project
Timing a HandoffYou are a competitive bicyclist. During a race, you bike at a constant velocity of k meters per second. A chase car waits for you at the ten-mile mark of a course. When you cross the ten-mile mark, the car immediately accelerates to catch you. The position function of the chase car is given by the equation s(t) = 15
4 t2 − 512t3, for 0 ≤ t ≤ 6, where t is the time in seconds and s is the distance
traveled in meters. When the car catches you, you and the car are traveling at the same velocity, and the driver hands you a cup of water while you continue to bike at k meters per second.
Exercises
1. Write an equation that represents your position s (in meters) at time t (in seconds).
2. Use your answer to Exercise 1 and the given information to write an equation that represents the velocity k at which the chase car catches you in terms of t.
3. Find the velocity function of the car.
4. Use your answers to Exercises 2 and 3 to find how many seconds it takes the chase car to catch you.
5. What is your velocity when the car catches you?
6. Use a graphing utility to graph the chase car’s position function and your position function in the same viewing window.
7. Find the point of intersection of the two graphs in Exercise 6. What does this point represent in the context of the problem?
8. Describe the graphs in Exercise 6 at the point of intersection. Why is this important for a successful handoff?
9. Suppose you bike at a constant velocity of 9 meters per second and the chase car’s position function is unchanged.
(a) Use a graphing utility to graph the chase car’s position function and your position function in the same viewing window.
(b) In this scenario, how many times will the chase car be in the same position as you after the 10-mile mark?
(c) In this scenario, would the driver of the car be able to successfully handoff a cup of water to you? Explain.
10. Suppose you bike at a constant velocity of 8 meters per second and the chase car’s position function is unchanged.
(a) Use a graphing utility to graph the chase car’s position function and your position function in the same viewing window.
(b) In this scenario, how many times will the chase car be in the same position as you after the ten-mile mark?
(c) In this scenario, why might it be difficult for the driver of the chase car to successfully handoff a cup of water to you? Explain.
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Preparation for Calculus
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P.2 Linear Models and Rates of Change
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3
Find the slope of a line passing through two points.
Write the equation of a line with a given point and slope.
Interpret slope as a ratio or as a rate in a real-life application.
Sketch the graph of a linear equation in slope-intercept form.
Write equations of lines that are parallel or perpendicular to a given line.
Objectives
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4
The Slope of a Line
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5
The slope of a nonvertical line is a measure of the number of units the line rises (or falls) vertically for each unit of horizontal change from left to right.
Consider the two points
(x1, y1) and (x2, y2) on the
line in Figure P.12.
Figure P.12
The Slope of a Line
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6
As you move from left to right along this line, a vertical change of
units corresponds to a horizontal change of
units. (The symbol ∆ is the uppercase Greek letter delta, and the symbols ∆y and ∆x are read “delta y” and “delta x.”)
The Slope of a Line
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7
The Slope of a Line
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8
When using the formula for slope, note that
So, it does not matter in which order you subtract as long as you are consistent and both “subtracted coordinates” come from the same point.
The Slope of a Line
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9
Figure P.13 shows four lines: one has a positive slope, one has a slope of zero, one has a negative slope, and one has an “undefined” slope.
In general, the greater the absolute value of the slope of a line, the steeper the line.
Figure P.13
The Slope of a Line
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10
Equations of Lines
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11
Equations of Lines
Any two points on a nonvertical line can be used to calculate its slope.
This can be verified from the similar triangles shown in Figure P.14.
Figure P.14
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12
Equations of Lines
If (x1, y1) is a point on a nonvertical line that has a slope of m and (x, y) is any other point on the line, then
This equation in the variables x and y can be rewritten in the form
y – y1 = m(x – x1)
which is called the point-slope form of the equation of a line.
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Equations of Lines
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Example 1 – Finding an Equation of a Line
Find an equation of the line that has a slope of 3 and passes through the point (1, –2). Then sketch the line.
Solution:
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Example 1 – Solution
Figure P.15
To sketch the line, first plot the point (1, –2). Then, because the slope is m = 3, you can locate a second point on the line by moving one unit to the right and three units upward, asshown in Figure P.15.
cont’d
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Ratios and Rates of Change
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Ratios and Rates of Change
The slope of a line can be interpreted as either a ratio or a rate.
If the x- and y-axes have the same unit of measure, then the slope has no units and is a ratio.
If the x- and y-axes have different units of measure, then the slope is a rate or rate of change.
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The maximum recommended slope of a wheelchair ramp is 1/12. A business installs a wheelchair ramp that rises to a height of 22 inches over a length of 24 feet, as shown in Figure P.16. Is the ramp steeper than recommended?
Example 2 – Using Slope as a Ratio
Figure P.16
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Example 2 – Solution
The length of the ramp is 24 feet or 12 (24) = 288 inches. The slope of the ramp is the ratio of its height (the rise) to its length (the run).
Because the slope of the ramp is less than ½ ≈ 0.083, the ramp is not steeper than recommended. Note that the slope is a ratio and has no units.
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The population of Oregon was about 3,831,000 in 2010 and about 3,970,000 in 2014. Find the average rate of change of the population over this four-year period. What will the population of Oregon be in 2024?
Solution:Over this four-year period, the average rate of change of the population of Oregon was
Example 3 – Using Slope as a Rate of Change
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Assuming that Oregon’s population continues to increase at this same rate for the next 10 years, it will have a 2024 population of about 4,318,000. (See Figure P.17.)
Example 3 – Solution
Figure P.17
Population of Oregon
cont’d
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Ratios and Rates of Change
The rate of change found in Example 3 is an average rate of change. An average rate of change is always calculated over an interval.
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Graphing Linear Models
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Graphing Linear Models
Many problems in analytic geometry can be classified in two basic categories:
1. Given a graph (or parts of it), find its equation.
2. Given an equation, sketch its graph.
For lines, problems in the first category can be solved by using the point-slope form. The point-slope form, however, is not especially useful for solving problems in the second category.
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Graphing Linear Models
The form that is better suited to sketching the graph of a line is the slope-intercept form of the equation of a line.
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Example 4 – Sketching Lines in the Plane
Sketch the graph of each equation.
a. y = 2x + 1
b. y = 2
c. 3y + x – 6 = 0
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Because b = 1, the y-intercept is (0, 1).
Because the slope is m = 2, you know that the line rises two units for each unit it moves to the right, as shown in Figure P.18(a).
Figure P.18(a)
Example 4(a) – Solution cont’d
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By writing the equation y = 2 in slope-intercept form
y = (0)x + 2
you can see that the slope is m = 0 and the y-intercept is (0,2). Because the slope is zero, you know that the line is horizontal, as shown in Figure P.18(b).
Figure P.18(b)
Example 4(b) – Solution cont’d
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Begin by writing the equation in slope-intercept form.
In this form, you can see that the y-intercept is (0, 2)
and the slope is m = This This means that the line falls one
unit for every three units it moves to the right.
Example 4(c) – Solution cont’d
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This is shown in Figure P.18(c).
Figure P.18(c)
Example 4(c) – Solution cont’d
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Because the slope of a vertical line is not defined, its equation cannot be written in the slope-intercept form. However, the equation of any line can be written in the general form
where A and B are not both zero. For instance, the vertical line
can be represented by the general form
Graphing Linear Models
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Graphing Linear Models
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Parallel and Perpendicular Lines
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Parallel and Perpendicular Lines
The slope of a line is a convenient tool for determining whether two lines are parallel or perpendicular, as shown in Figure P.19.
Figure P.19
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Parallel and Perpendicular Lines
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Example 5 – Finding Parallel and Perpendicular Lines
Find the general forms of the equations of the lines that pass through the point (2, –1) and are
(a) parallel to the line2x – 3y = 5
(b) perpendicular to the line2x – 3y = 5.
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Example 5 – Solution
Begin by writing the linear equation 2x – 3y = 5 in
slope-intercept form.
So, the given line has a slope
of (See Figure P.20.)
Figure P.20
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Example 5 – Solution
a. The line through (2, –1) that is parallel to the given line also has a slope of 2/3.
Note the similarity to the equation of the given line,2x – 3y = 5.
cont’d
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Example 5 – Solution
b. Using the negative reciprocal of the slope of the given line, you can determine that the slope of a line perpendicular to the given line is –3/2.
cont’d
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